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Premise-1 Tsionawit is Ethiopian. Premise2 Zelalem is an African. Premise-2 Therefore, Tsionawit is African. Conclusion Therefore, Zelalem is black. Conclusion In both arguments, the first two statements are premises, because they are claimed to provide evidence for the third statement, whereas the third statement is a conclusion because it is claimed to follow from the given evidences.

The former are said to be good well-supported arguments, the latter bad poorly-supported arguments. For example, compare the above two examples. In the first argument, the premises really do support the conclusion, they give good reason for believing that the conclusion is true, and therefore, the argument is a good one. But the premises of the second argument fail to support the conclusion adequately.

Even if they may be true, they do not provide good reason to believe that the conclusion is true. Therefore, it is bad argument, but it is still an argument.

But how can we distinguish premises from conclusion and vice versa? Despite the purpose of logic, as the science that evaluates and analyses arguments, is to develop methods and techniques that allow us to distinguish good arguments from bad, one of the most important tasks in the analysis of arguments is to distinguish premises from conclusion and vice versa. Sometimes identifying a conclusion from premises is very tough. Premises and conclusions are difficult to identify for a number of reasons.

Even though all arguments are By: Teklay G. Moreover, even though it is assumed, for the sake of argument, that all arguments are composed of premises and conclusion, identifying conclusion from argument is very difficult. Since it is impossible to analyze arguments without identifying a conclusion from premises, we need techniques that can help us to identify premises from a conclusion and vice versa. The first technique that can be used to identify premises from a conclusion and vice versa is looking at an indicator word.

Frequently, arguments contain certain indicator words that provide clues in identifying premises and conclusion. Here below are some Conclusion Indicators: Therefore We may conclude Thus So Wherefore Entails that Consequently It follows that Accordingly Hence We may infer Provided that It shows that It implies that It must be that Whence As a result In argument that contains any of the conclusion indicator words, the statement that follows the indicator word can usually be identified as the conclusion.

By the process of elimination, the other statements in the argument can be identified as premises, but only based on their logical importance to the identified conclusion. Example: Women are mammals. Zenebech is a woman. Therefore, Zenebech is a mammal. If an argument does not contain a conclusion indicator, it may contain a premise indicator. By same the process of elimination, the other remaining single statement will be a conclusion. Example: You should avoid any form of cheating on exams because cheating on exams is punishable by the Senate Legislation of the University.

We can say that in the middle place between the premise and the conclusion, this indicator can be both premise and conclusion indicator. Consider the following argument: Tsionawit is a faithful wife, for Ethiopian women are faithful wives and Tsionawit an Ethiopian. These are the premises. Sometimes you may an argument that contains no indicator all: neither a conclusion indicator word nor a premise indicator word.

The answers to these questions should point to the conclusion. Example: Our country should increase the quality and quantity of its military. Ethnic conflicts are recently intensified; boarder conflicts are escalating; international terrorist activities are increasing. The main point of this argument is to show that the country should increase the size and quality of its military. All the rest are given in support of the conclusion.

As you can see there are no indicator words. The following is the standard form of this argument: Ethnic conflicts are recently intensified.

P-1 Boarder conflicts are escalating. P-2 International terrorist activities are increasing. P-3 Thus, the country should increase the quality and quantity of its military. C Passages that contain arguments sometimes contain statements that are neither premises nor conclusion. Only statements that are actually intended to support the conclusion should be included in the list of premises.

If a statement has nothing to do with the conclusion or, for example, simply makes a passing comment, it should not be included within the context of the argument. In addition, it might very well bankrupt the federal treasury. This is the whole case against socialized medicine in a nutshell. The last statement makes only a passing comment about the argument itself and is therefore neither a premise nor a conclusion. Inference is another concept.

In the narrower sense it means the reasoning process expressed by the argument. And broadly it refers the argument itself. For the purpose of this course, we use the narrower sense of the term inference or inferential link between the premises and the conclusion of arguments. Lesson 2: Techniques of Recognizing Arguments Lesson Overview An argument is a systematic combination of one or more than one statements, which are claimed to provide a logical support or evidence i.

However, not all passages that contain two or more statements are argumentative. There are various passages that contain two or more statements but are not argumentative. Argumentative arguments are distinguished from such kind of passages by their primary goal: proving something.

In this lesson, we will see the techniques of distinguishing argumentative passages from non- argumentative passages. What qualifies a passage to be an argument? Evaluating arguments about different issues in human life like those that address, religion, politics, ethics, sport, science, love, culture, environment, society, culture etc. Therefore, as logicians, in order to evaluate arguments easily, we need to understand the nature of arguments and further we need to understand what argument is not, because not all passages contain argument.

Since logic deals with arguments, it is important for students to develop the ability to identify whether passages contain an argument. In a general way, a passage contains an argument if it purports to prove something; if it does not do so, it does not contain an argument.

But what does it mean to purport to prove something? Two conditions must be fulfilled for a passage to purport to prove something: 1 At least one of the statements must claim to present evidence or reasons. As we have seen earlier, the statements that claim to present the evidence or reasons are the premises and the statement that the evidence is claimed to support or imply is the conclusion. Hence, the first condition refers to premises as it tries to provide or claim to provide reasons or evidences for the conclusion; and the second condition refers to a conclusion.

It is not necessary that the premises present actual evidence or true reasons nor that the premises actually do support the conclusion. But at least the premises must claim to present evidence or reasons, and there must be a claim that the evidence or reasons support or imply something. Thus, most of our attention will be concentrated on whether the second condition is fulfilled.

The second condition expresses what is called an inferential claim. Also, you should recognize that this claim is not equitable with the intentions of the arguer. Intentions are subjective and, as such, are usually not accessible to the evaluator. Rather, the inferential claim is an objective feature of an argument grounded in its language or structure. In evaluating arguments, therefore, most of our attention will be concentrated on whether the second condition is fulfilled because it is not necessary, at least at this level, that the premises present actual evidence or true reasons nor that do the premises actually support the conclusion.

An inferential claim can be either explicit or implicit. It exists if there is an indicator word that asserts an explicit relationship between the premises and the conclusions. Example: Gamachuu is my biological father, because my mother told so.

Hence, the passage is an argument. An implicit inferential claim exists if there is an inferential relationship between the statements in a passage, but the passage contains no indicator words.

Example: The genetic modification of food is risky business. Genetic engineering can introduce unintended changes into the DNA of the food-producing organism, and these changes can be toxic to the consumer.

In deciding whether there is a claim that evidence supports or implies something keep an eye out for 1 indicator words, and 2 the presence of an inferential claim between the statements. In connection with these points, however, a word of caution is in order.

First, the mere occurrence of an indicator word by no means guarantees the presence of an argument. The presence of an indicator word does not mean that the existing indicator word actually and always indicate a premises or a conclusions. Thus, before deciding that an indicator word indicates a premises or a conclusion, make sure that the existing indicator word is used to indicate a premise or a conclusion. Example: Since Edison invented the phonograph, there have been many technological developments.

Since Edison invented the phonograph, he deserves credit for a major technological development. Second, it is not always easy to detect the occurrences of an inferential relationship between statements in a passage, and the reader may have to review a passage several times before making a decision. Therefore, in deciding whether a passage contains an argument one should try to insert mentally some indicators words among the statements to see whether there is a flow of ideas among the statements.

Even with this mental experiment, however, deciding whether a passage contains an argument is very difficult. As a result, not everyone will agree about every passage. What do they lack to be arguments? Having seen what arguments are and how we recognize them, we will now focus on what arguments are not and how we recognize them.

Non-argumentative passages are passages, which lack an inferential claim. These include simple non-inferential passages, expository passages, illustrations, explanations, and conditional statements. Passages that lack an inferential claim may be statements, which could be premises, conclusion, or both. What is missed is a claim that a reasoning process is being made. As was discussed previously, for a passage to be an argument, it not only should contain premises and a conclusion but also an inferential claim or a reasoning process.

In this portion of our lesson, we will discuss some of the most important forms of non-argumentative passages. Simple Non-inferential Passages Simple non-inferential passages are unproblematic passages that lack a claim that anything is being proved. Such passages contain statements that could be premises or conclusions or both , but what is missing is a claim that any potential premise supports a conclusion or that any potential conclusion is supported by premises.

Passages of this sort include warnings, pieces of advice, statements of belief or opinion, loosely associated statements, and reports. A warning is a form of expression that is intended to put someone on guard against a dangerous or detrimental situation. Example: Whatever you promise to tell, never confide political secrets to your wife.

In this passage, no evidence is given to prove that the statement is true; and if no evidence is given to prove that the statement is true, then there is no argument.

Example: After class hours, I would suggest that you give careful consideration to the subject matter you have discussed. As with warnings, there is no evidence that is intended to prove anything in piece of advices, and hence there is no argument in the above passage. A statement of belief or opinion is an expression about what someone happens to believe or think about something. Example: We believe that our university must develop and produce outstanding students who will perform with great skill and fulfill the demands of our nation.

This passage does not make any claim that the belief or opinion is supported by evidence, or that it supports some conclusion, and hence does not contain an argument. Loosely associated statements may be about the same general subject, but they lack a claim that one of them is proved by the others.

Example: Not to honor men of worth will keep the people from contention; not to value goods that are hard to come by will keep them from theft; not to display what is desirable will keep them from being unsettled of mind. Lao-Tzu, Thoughts from the Tao Te Ching Because there is no claim that any of these statements provides evidence or reasons for believing another, there is no argument.

Example: The great renaissance dam of Ethiopia has opened an employment opportunity for thousands of Ethiopians. In its completion, thirteen thousand Ethiopians are expected to be hired. These statements could serve as the premises of an argument, but because the author makes no claim that they support or imply anything, there is no argument. One must be careful, though, with reports about arguments.

Newspaper clipping Properly speaking, this passage is not an argument, because the author of the passage does not claim that anything is supported by evidence. Expository Passages An expository passage is a kind of discourse that begins with a topic sentence followed by one or more sentences that develop the topic sentence. If the objective is not to prove the topic sentence but only to expand it or elaborate it, then there is no argument. Example: There is a stylized relation of artist to mass audience in the sports, especially in baseball.

Each player develops a style of his own-the swagger as he steps to the plate, the unique windup a By: Teklay G. This passage is not argument, because it lacks an inferential claim. Example: Skin and the mucous membrane lining the respiratory and digestive tracts serve as mechanical barriers to entry by microbes.

Oil gland secretions contain chemicals that weaken or kill bacteria on skin. The respiratory tract is lined by cells that sweep mucus and trapped particles up into the throat, where they can be swallowed.

The stomach has an acidic pH, which inhibits the growth of many types of bacteria. Sylvia S. Mader, Human Biology, 4th ed. Thus, the passage can be taken as both an expository passage and an argument. In deciding whether an expository passage should be interpreted as an argument, try to determine whether the purpose of the subsequent sentences in the passage is merely to develop the topic sentence or also to prove that it is true.

In borderline cases, ask yourself whether the topic sentence makes a claim that everyone accepts or agrees with. If it does, the passage is probably not an argument. In real-life situations, authors rarely try to prove something is true when everyone already accepts it. However, if the topic sentence makes a claim that many people do not accept or have never thought about, then the purpose of the remaining sentences may be both By: Teklay G.

If this be so, the passage is an argument. Illustrations An illustration is an expression involving one or more examples that is intended to show what something means or how it is done. This passage is not an argument, because it makes no claim that anything is being proved. However, as with expository passages, many illustrations can be taken as arguments. Such arguments are often called arguments from example. Here is an instance of one: Although most forms of cancer, if untreated, can cause death, not all cancers are life- threatening.

For example, basal cell carcinoma, the most common of all skin cancers, can produce disfigurement, but it almost never results in death. In deciding whether an illustration should be interpreted as an argument, determine whether the passage merely shows how something is done or what something means, or whether it also purports to prove something. In borderline cases, it helps to note whether the claim being illustrated is one that practically everyone accepts or agrees with.

If it is, the passage is probably By: Teklay G. As already noted, in real-life situations, authors rarely attempt to prove what everyone already accepts.

But if the claim being illustrated is one that many people do not accept or have never thought about, then the passage may be interpreted as an argument.

For example, practically everyone knows that water is H2O. But they may not have ever considered whether some forms of cancer are not life- threatening. Explanations One of the most important kinds of non-argument is the explanation. An explanation is an expression that purports to shed light on some event or phenomenon, which is usually accepted as a matter of fact.

It attempts to clarify, or describe such alike why something is happen that way or why something is what it is. Example: Cows digest grass while humans cannot, because their digestive systems contain enzyme not found in humans. Every explanation is composed of two distinct components: the explanandum and explanans. The explanandum is the statement that describes the event or phenomenon to be explained, and the explanans is the statement or group of statements that purports to do the explaining.

In other words, the purpose of the explanans is to show why something is the case, whereas in an argument, the purpose of the premises is to prove that something is the case. That is, the premise refer to an accepted fact, and intended to prove that something is the case, while the conclusion is a new assertion followed from the already known fact.

Moreover, in explanation, we precede backward from fact to the cause whereas in argument we move from premise to the conclusion. In the above example given, the fact that cows digest grass but humans cannot is readily apparent to everyone. Explanations bear a certain similarities to an argument. The rational link between the explanandum and explanans may at times resemble the inferential link between the premise and the conclusion of an argument.

If this statement describes an accepted matter of fact, and if the remaining statements purport to shed light on this statement, then the passage is an explanation. This method usually works to distinguish arguments from explanations. However, some passages can be interpreted as both explanations and arguments. Example: Women become intoxicated by drinking a smaller amount of alcohol than men because men metabolize part of the alcohol before it reaches the bloodstream, whereas women do not.

Alternately, the passage could be By: Teklay G. Thus, this passage can be correctly interpreted as both an explanation and an argument. Obviously, what is accepted by one person may not be accepted by another. Sometimes the source of the passage textbook, newspaper, technical journal, etc. But when the passage is taken totally out of context, ascertaining the source may prove impossible. In those circumstances the only possible answer may be to say that if the passage is an argument, then such-and-such is the conclusion and such-and-such are the premises.

Every conditional statement is made up of two component statements. However, there is an occasion that the order of antecedent and consequent is reversed. However, such a relationship need not exist for a statement to count as conditional. Consequent Antecedent if Conditional statements are not arguments, because they fail to meet the criteria given earlier.

In an argument, at least one statement must claim to present evidence, and there must be a claim that this evidence implies something. In a conditional statement, there is no claim that either the antecedent or the consequent presents evidence. In other words, there is no assertion that either the antecedent or the consequent is true. Rather, there is only the assertion that if the antecedent is true, then so is the consequent. It does not assert that you study hard. Of course, a conditional statement as a whole may present evidence because it asserts a relationship between statements.

Yet when conditional statements are taken in this sense, there is still no argument, because there is then no separate claim that this evidence implies anything. Therefore, a single conditional statement is not an argument. That is why also conditional statements are not evaluated as true or false without separately evaluating the antecedent and the consequent.

They only claim that if the antecedent is true then so is the consequent. However, some conditional statements are similar to arguments in that they express the outcome of a reasoning process. As such, they may be said to have a certain inferential content. Consider the following example: If destroying a political competitor gives you joy, then you have a low sense of morality. Accordingly, conditional statements are not arguments. Yet, although taken by themselves are not arguments, their inferential content, the inferential content between the antecedent and the consequent , may be re-expressed to form arguments.

For example, the conditional statement can be re-expressed to form an argument as follows: Destroying a political competitor gives you joy.

Therefore, you have a low sense of morality. Here, we clearly have a premise and conclusion structure, and the conclusion is asserted on the basis of the premise.

Therefore, it is argument. Finally, while no single conditional statement is an argument, a conditional statement may serve as either the premise or the conclusion or both of an argument.

Observe the following examples: If he is selling our national secretes to enemies, then he is a traitor. He is selling our national secretes to enemies. Therefore, he is a traitor. If he is selling our national secretes to enemies, then he is a traitor.

If he is a traitor, then he must be punished by death. Therefore, If he is selling our national secretes to enemies, then he must be punished by death. The relation between conditional statements and arguments may now be summarized as follows: 1 A single conditional statement is not an argument.

But if it consists of a conditional statement together with some other statement, then, by the second rule, it may be an argument, depending on such factors as the presence of indicator words and an inferential relationship between the statements.

A is said to be a sufficient condition for B whenever the occurrence of A is all that is needed for the occurrence of B. For example, being a dog is a sufficient condition for being an animal. On the other hand, B is said to be a necessary condition for A whenever A cannot occur without the occurrence of B.

Thus, being an animal is a necessary condition for being a dog. The difference between sufficient and necessary conditions is a bit tricky. So, to clarify the idea further, suppose you are given a large, closed cardboard box. Also, suppose you are told that there is a dog in the box. Then you know for sure, there is an animal in the box. No additional information is needed to draw this conclusion.

This means that being a dog is sufficient for being an animal. However, being a dog is not necessary for being an animal, because if you are told that the box contains a cat, you can conclude with equal certainty that it contains an animal. In other words, it is not necessary for the box to contain a dog for it to contain an animal.

It might equally well contain a cat, a mouse, a squirrel, or any other animal. On the other hand, suppose you are told that whatever might be in the box, it is not an animal.

Then you know for certain there is no dog in the box. The reason you can draw this conclusion is that being an animal is necessary for being a dog. If there is no animal, there is no dog. However, being an animal is not sufficient for being a dog, because if you are told that the box contains an animal, you cannot, from this information alone, conclude that it contains a dog. It might contain a cat, a mouse, a squirrel, and so on.

These ideas are expressed in the following conditional statements: If X is a dog, then X is an animal. If X is not an animal, then X is not a dog. Thus, each expresses in one way a necessary condition and in another way a sufficient condition.

A is a sufficient condition for B; if A occurs, then B must occur. Note: A is a necessary condition for B; if B occur, then A must occur. In general, non-argumentative passages may contain components that resemble the premises and conclusions of arguments, but they do not have an inferential claim.

However, some passages like expository passages, illustrations, and explanations can be interpreted as arguments; and the inferential contents of conditional statements may be re-expressed to form arguments. But remember that the mere occurrence of an indicator word does not guarantee the presence of an argument.

Lesson 3: Types of Arguments: Deduction and Induction Lesson Overview In our previous lesson, we saw that every argument involves an inferential claim- the claim that the conclusion is supposed to follow from the premises. Every argument makes a claim that its premises provide grounds for the truth of its conclusion. The question we now address has to do By: Teklay G. Just how strongly is the conclusion claimed to follow from the premises.

The reasoning process inference that an argument involves is expressed either with certainty or with probability. That is what the logician introduced the name deduction and induction for, respectively. If the conclusion is claimed to follow with strict certainty or necessity, the argument is said to be deductive; but if it is claimed to follow only probably, the argument is said to be inductive.

Therefore, a conclusion may be supported by its premise in two very different ways. These two different ways are the two great classes of arguments: Deductive arguments and Inductive arguments. And the distinction between these two classes of arguments, because every argument involves an inferential claim, lies in the strength of their inferential claim.

Understanding the distinction of these classes is essential in the study of logic. In this lesson, we will learn the broad groups of arguments, Deductive arguments and Inductive arguments, and the techniques of distinguishing one from the other.

A deductive argument is an argument incorporating the claim that it is impossible for the conclusion to be false given that the premises are true. It is an argument in which the premises are claimed to support the conclusion in such a way that it is impossible for the premises to be true and the conclusion false.

In such arguments, the conclusion is claimed to follow necessarily conclusively from the premises. Thus, deductive arguments are those that involve necessary reasoning. All African footballers are blacks. Socrates is a philosopher. Messi is an African footballer. Therefore, Socrates is a critical thinker. It follows that, Messi is black. The above two examples are examples of a deductive argument.

In both of them, the conclusion is claimed to follow from the premises with certainty; or the premises are claimed to support their corresponding conclusion with a strict necessity.

If we, for example, assume that all philosophers are critical thinkers and that Socrates is a philosopher, then it is impossible that Socrates not be a critical thinker. Similarly, if we assume that all African footballers are blacks and that Messi is an African footballer, then it is impossible that Messi not be a black.

Thus, we should interpret these arguments as deductive. An inductive argument is an argument incorporating the claim that it is improbable for the conclusion to be false given that the premises are true.

It is an argument in which the premises are claimed to support the conclusion in such a way that it is improbable for the premises to be true and the conclusion false.

In such arguments, the conclusion is claimed to follow only probably from the premises. The premises may provide some considerable evidence for the conclusion but they do not imply necessarily support the conclusion. In this case, we might have sufficient condition evidence but we cannot be certain about the truth of the conclusion. However, this does not mean that the conclusion is wrong or unacceptable, where as it could be correct or acceptable but only based on probability.

Thus, inductive arguments are those that involve probabilistic reasoning. Almost all women are mammals. Mandela was an African leader. Hanan is a woman. Therefore, probably Mandela was black. Hence, Hanan is a mammal. Both of the above arguments are inductive. In both of them, the conclusion does not follow from the premises with strict necessity, but it does follow with some degree of probability. That is, the conclusion is claimed to follow from the premises only probably; or the premises are claimed to support their corresponding conclusion with a probability.

In other words, if we assume that the premises are true, then based on that assumption it is probable that the conclusion is true. If we, for example, assume that most African leaders were blacks and that Mandela was an African leader, then it is improbable that Mandela not been a black, or it is probable that Mandela was black.

But it is not impossible that Mandela not been a black. Similarly, if we assume that almost all women are mammals and that Hanan is a woman, then it is improbable that Hanan not be a mammal, or it is probable that Hanan is a mammal. But it is not impossible that Hanan not be a mammal. Thus, the above arguments are best interpreted as inductive. In other words, the distinction lies on how strongly the conclusion is claimed to follow from the premises, or how strongly the premises are claimed to support the conclusion.

However, in most arguments, the strength of this claim is not explicitly stated, so we must use our interpretative abilities to evaluate it.

In the deciding whether an argument is deductive or inductive, we must look at certain objective features of the argument. These are: By: Teklay G. However, we must acknowledge at the outset that many arguments in ordinary language are incomplete, and because of this, deciding whether the argument should best be interpreted as deductive or inductive may be impossible.

Let us see the above factors in detail in order to understand and identify the different styles of argumentation. The first factor that influences our decision about a certain inferential claim is the occurrence of special indicator words. There are different sort of indicator words that indicate or mark the type of a certain argument. The point is that if an argument draws its conclusion, using either of the deductive indicator words, it is usually best to interpret it as deductive, but if it draws its conclusion, using either of the inductive indicator words, it is usually best to interpret it as inductive.

Deductive and Inductive indicator words often suggest the correct interpretation. However, one should be cautious about these special indicator words, because if they conflict with one of the other criteria, we should probably ignore them.

If one takes these words at face value, then one might wrongly leads into wrong conclusions. Therefore, the occurrence of an indicator word By: Teklay G. This leads us to consider the second factor.

The second factor that bears upon our interpretation of an argument as inductive or deductive is the actual strength of the inferential link between premises and conclusion. If the conclusion actually does follow with strict necessity from the premises, the argument is clearly deductive.

In such an argument, it is impossible for the premises to be true and the conclusion false. If, on the other hand, the conclusion of an argument does not follow with strict necessity but does follow probably, it is usually best to interpret it as inductive argument.

Consider the following examples. Example Example All Ethiopian people love their country. The majority of Ethiopian people are poor. Debebe is an Ethiopian. Alamudin is an Ethiopian. Therefore, Debebe loves his country. Therefore, Alamudin is poor. If we assume that all Ethiopian people love their country and that Debebe is an Ethiopian, then it is impossible that Debebe not love his country.

Thus, we should interpret this argument as deductive. In the second example, the conclusion does not follow from the premises with strict necessity, but it does follow with some degree of probability. If we assume that the premises are true, then based on that assumption it is probable that the conclusion is true. Thus, it is best to interpret the second argument as inductive. Occasionally, an argument contains no special indicator words, and the conclusion does not follow either necessarily or probably from the premises; in other words, it does not follow at all.

This situation points up the need for the third factor to be taken into account, which is the character or form of argumentation the arguer uses.

Let us see some examples of deductive argumentative forms and inductive argumentative forms. Argument based on mathematics: it is an argument in which the conclusions depend on some purely arithmetic or geometric computation or measurement. For example, you can put two orange and three bananas in a bag and conclude that the bag contains five fruits. Or again you can measure a square pieces of land and after determining it is ten meter on each side conclude that its area is a hundred square meter.

Since all arguments in pure mathematics are deductive, we can usually consider arguments that depend on mathematics to be deductive as well. A noteworthy exception, however, is arguments that depend on statistics are usually best interpreted as inductive. Arguments based on definition: it is an argument in which the conclusion is claimed to depend merely up on the definition of some words or phrase used in the premise or conclusion.

For example, one may argue that Angel is honest; it is follows that Angel tells the truth. Or again, Kebede is a physician; therefore, he is a doctor. Syllogisms are arguments consisting of exactly two premises and one conclusion.

Syllogisms can be categorized into three groups; categorical, hypothetical, and disjunctive syllogism. Categorical syllogism: a syllogism is an argument consisting of exactly two premises and one conclusion.

Example: All Egyptians are Muslims. No Muslim is a Christian. Arguments such as these are nearly interpreted as deductive. Hypothetical syllogism: It is a syllogism having a conditional statement for one or both of its premises.

Example: If you study hard, then you will graduate with Distinction. If you graduate with Distinction, then you will get a rewarding job. Therefore, if you study hard, then you will get a rewarding job. Such arguments are best interpreted as deductive. Disjunctive syllogism: it is a syllogism having a disjunctive statement. Example: Rewina is either Ethiopian or Eritrean. Rewina is not Eritrean. Therefore, Rewina is Ethiopian. As with hypothetical syllogism, such arguments are usually best taken as deductive.

The premises of such an argument typically deal with some subject that is relatively familiar, and the conclusion then moves beyond this to a subject that is less familiar or that little is known about. Such an argument may take any of several forms: predictions about the future, arguments from analogy, inductive generalizations, arguments from authority, arguments based on signs, and causal inferences, to name just a few.

For example, one may argue that because certain clouds develop in the center of the highland, a rain will fall within twenty-four hours. Nearly everyone realizes that the future cannot be known with certainty. Thus, whenever an argument makes a prediction about the future one is usually justified considering the argument inductive.

An argument from analogy: It is an argument that depends on the existence of an analogy or similarity between two things or state of affairs. Because of the existence of this analogy a certain conditions that affects the better- known thing or situations is concluded to affect the less familiar , lesser known-thing or situation. For instance, one may conclude, after observing the similarity of some features of Computer A and car B: that both are manufactured in ; that both are easy to access; that Computer A is fast in processing; it follows that Computer B is also fast in processing.

This argument depends on the existence of a similarity or analogy between the two cars. The certitude attending such an inference is obviously probabilistic at best.

An inductive generalization: it is an argument that proceeds from the knowledge of a selected sample to some claim about the whole group. Because the members of the sample have a certain characteristics, it is argued that all members of the group have the same characteristics. For example, one may argue that because three out of four people in a single prison are black, one may conclude that three-fourth of prison populations are blacks.

This example illustrate the use of statistics in inductive argumentation. An argument from authority: it is an argument in which the conclusions rest upon a statement made by some presumed authority or witness. A lawyer, for instance, may argue that the person is guilty because an eyewitness testifies to that effect under oath.

Because the professor and the eyewitness could be either mistaken or lying, such arguments are essentially probabilistic. Arguments based on sign: it is an argument that proceeds from the knowledge of a certain sign to the knowledge of a thing or situation that the sign symbolizes.

For instance, one may infer that By: Teklay G. But because the sign might be displaced or in error about the area or forgotten, conclusion follows only probably. A causal inference: it is an argument which proceed from the knowledge of a cause to the knowledge of an effect, or conversely, from the knowledge of an effect to knowledge of a cause. Because specific instances of cause and effect can never be known with absolute certainty, one may usually interpret such an argument as inductive.

Furthermore Considerations It should be noted that the various subspecies of inductive arguments listed here are not intended to be mutually exclusive. Overlaps can and do occur. For example, many causal inferences that proceed from cause to effect also qualify as predictions. We should take care not to confuse arguments in geometry, which are always deductive, with arguments from analogy or inductive generalizations. For example, an argument concluding that a triangle has a certain attribute such as a right angle because another triangle, with which it is congruent, also has that attribute might be mistaken for an argument from analogy.

One broad classification of arguments not listed in this survey is scientific arguments. Arguments that occur in science can be either inductive or deductive, depending on the circumstances. In general, arguments aimed at the discovery of a law of nature are usually considered inductive. Another type of argument that occurs in science has to do with the application of known laws to specific circumstances. Arguments of this sort are often considered to be deductive, but only with certain reservations.

A final point needs to be made about the distinction between inductive and deductive arguments. There is a tradition extending back to the time of Aristotle that holds that inductive arguments are those that proceed from the particular to the general, while deductive arguments are those By: Teklay G. A particular statement is one that makes a claim about one or more particular members of a class, while a general statement makes a claim about all the members of a class.

In fact, there are deductive arguments that proceed from the general to the general, from the particular to the particular, and from the particular to the general, as well as from the general to the particular; and there are inductive arguments that do the same. For example, here is a deductive argument that proceeds from the particular to the general: Three is a prime number.

Five is a prime number. Seven is a prime number. Therefore, all odd numbers between two and eight are prime numbers. Here is an inductive argument that proceeds from the general to the particular: All emeralds previously found have been green. Therefore, the next emerald to be found will be green. In sum up, to distinguish deductive arguments from inductive, we look for special indicator words, the actual strength of the inferential link between premises and conclusion, and the character or form of argumentation.

Lesson 4: Evaluating Arguments Lesson Overview In our previous lesson, we have seen that every argument makes two basic claims: a claim that evidence or reasons exist and a claim that the alleged evidence or reasons support something or that something follows from the alleged evidence or reasons.

The first is a factual claim, and the second is an inferential claim. The evaluation of every argument centers on the evaluation of these two claims. The most important of the two is the inferential claim, because if the premises fail to support the conclusion that is, if the reasoning is bad , an argument is worthless. Thus, we will always test the inferential claim first, and only if the premises do support the conclusion will we test the factual claim that is, the claim that the premises present genuine evidence, or are true.

In this By: Teklay G. And the primary purpose of this lesson is to introduce you with the natures of good arguments both in deductive and inductive arguments. Hence, you will learn effective techniques and strategies for evaluating arguments.

How do you think are the validity and soundness of a deductive argument evaluated? Deduction and Validity The previous section defined a deductive argument as one in which the premises are claimed to support the conclusion in such a way that if they are assumed true, it is impossible for the conclusions to be false. If the premises do in fact support the conclusions in this way the arguments is said to be valid; if not, it is invalid.

Thus, a valid deductive argument is an argument such that if the premises are assumed true, it is impossible for the conclusion to be false. In such arguments, the conclusion follows with strict necessity from the premises. Conversely, an invalid deductive argument is an argument such that if the premises are assumed true, it is possible for the conclusion to be false. In these arguments, the conclusion does not follow with strict necessity from the premises, even though it is claimed to.

Consider the following examples: Example All men are mammals. All philosophers are rational. Therefore, all bulls are mammals. Socrates was rational. Therefore, Socrates was a philosopher. Example The first example is valid argument, because the conclusion actually followed from the premises with a strict necessity. If all men are assumed as mammals and bulls as men, then it is impossible for bulls not be mammals.

Hence, the argument is valid. The second example is invalid argument, because the conclusion did not actually follow from the premises with a strict necessity, even though it is claimed to. That is, even if we assume that all philosophers rational and Socrates is rational, it is not actually impossible for Socrates not be a philosopher. The above definitions of valid and invalid arguments, along with their corresponding examples, lead us into two immediate conclusions.

The first is that there is no middle ground between valid and invalid. An argument is either valid or invalid. The second consequence is that there is only an indirect relation between validity and truth. For an argument to be valid it is not necessary that either the premises or the conclusions be true, but merely that if the premises assumed true, it is impossible for the conclusion be false.

That is, we do not have to know whether the premise of an argument is actually true in order to determine its validity valid or invalid. To test an argument for validity, we begin by assuming that all premises are true, and then we determine if it is possible, in light of that assumption, for the conclusion to be false. Thus, the validity of argument is the connection between premise and conclusion rather than on the actual truth or falsity of the statement formed the argument.

There are four possibilities with respect to the truth or falsity of the premises and conclusion of a given argument: 1 True premises and True conclusion, 2 True premises and False conclusion, 3 False premises and True conclusion, and 4 False premises and False conclusion.

Note that all of the above possibilities, except the second case true premises and false conclusion , allow for both valid and invalid arguments. That is, the second case does not allow By: Teklay G. As we have just seen, any argument having this combination is necessarily invalid. Let us discuss these possibilities in detail with examples. Validity and Truth Value Possibility 1: A combination of True premises and True conclusion the first case allows for both valid and invalid arguments.

Tp All philosophers are critical thinkers. Tp My mother is a mammal. Tp Plato was a critical thinker. Tp Therefore, my mother is a woman. Tc Therefore, Plato was a philosopher.

Tc Based on the features of valid and invalid arguments, the above two examples, each of which combine True premises and True conclusion, are valid argument and invalid argument, respectively.

Therefore, the first combination allows for both valid and invalid arguments. Possibility 2: A combination of True premises and false conclusion the second case allows only for invalid arguments. Consider the following example: Example-1 Invalid : All biologists are scientists. Tp John Nash was a scientist. Tp Therefore, John Nash was a biologist. Fc Based on the features of validity, the above example, which combines True premises and False conclusion, is an invalid argument.

A valid argument with such combination does not exist. Any deductive argument having actually true premises and an actually false conclusion is invalid, because if the premises are actually true and the conclusion is actually false, then it certainly is possible for the premises to be true and the conclusion false.

Thus, by definition, the argument is invalid. After all such combinations are contrary to the inferential claim of a deductive argument: By: Teklay G.

Therefore, the second combination allows only for invalid arguments. Possibility 3: A combination of False premises and True conclusion the third case allows for both valid and invalid arguments. Fp All birds are mammals. Fp All women are birds. Fp All ostriches are mammals. Fp Therefore, all women are mammals.

Tc Therefore, all ostriches are birds. Tc Based on the features of valid and invalid arguments, the above two examples, each of which combine False premises and True conclusion, are valid argument and invalid argument, respectively. Therefore, the third combination, as the first one, allows for both valid and invalid arguments.

Possibility 4: A combination of False premises and False conclusion the fourth case allows for both valid and invalid arguments. Fp All Egyptians are Americans. Fp All ants are mammals. Fp Thus, all Egyptians are Ethiopians. Fc Therefore, all ants are birds. Fc Based on the features of valid and invalid arguments, the above two examples, each of which combine False premises and False conclusion, are valid argument and invalid argument, respectively.

Therefore, the fourth combination also allows for both valid and invalid arguments. In general, the basic idea of evaluating deductive argument, validity valid and invalid is not something that is determined by the actual truth or falsity of the premises and conclusion.

Rather, validity is something that is determined by the relationship between premises and conclusion. The question is not whether premises and conclusion are true or false, but whether the premises By: Teklay G.

Nevertheless, there is one arrangement of truth and falsity in the premises and conclusion that does determine the issue of validity. Any deductive argument having actually true premises and an actually false conclusion is invalid for the reason given above. The idea that any deductive argument having actually true premises and a false conclusion is invalid may be the most important point in the entire system of deductive logic.

The entire system of deductive logic would be quite useless if it accepted as valid any inferential process by which a person could start with truth in the premises and arrive at falsity in the conclusion.

The relationship between the validity of a deductive argument and the truth and falsity of its premises and conclusions summarized as follows. Table 1. We have also said that we will always test the inferential claim first, and only if the premises do support the conclusion will we test the factual claim that is, the claim that the premises present genuine evidence, or are true.

Now that we have tested the inferential claims of deductive arguments, it is time to proceed to the next step: evaluating the factual claims of deductive arguments. Depending on their actual ability, assuming that they already have actually accomplished their inferential claims by being valid , to accomplish their factual claims, deductive arguments can be either sound or unsound.

A sound argument is a deductive argument that is valid and has all true premises. Both conditions must be met for an argument to be sound, and if either is missing the By: Teklay G. A deductive argument that does not actually accomplish its inferential claim, that is not valid , cannot be sound, regardless of the truth values of its premises. Such a deductive argument is unsound, by definition. Thus, an unsound argument is a deductive argument that is either valid with one or more false premises, or invalid, or both.

Because a valid argument is one such that it is impossible for the premises to be true and the conclusion false, and because a sound argument does in fact have true premises, it follows that every sound argument, by definition, will have a true conclusion as well. How do you think are the strength and cogency of an inductive argument evaluated? Induction and Strength The previous section defined an inductive argument as one in which the premises are claimed to support the conclusions in such a way that if they are assumed true, it is improbable for the conclusions to be false.

If the premises do in fact support the conclusions in this way the arguments is said to be strong; if not, it is weak. Thus, a strong inductive argument is an argument such that if the premises are assumed true, it is improbable for the conclusion to be false.

In such arguments, the conclusion follows probably from the premises. Conversely, a weak inductive argument is an argument such that if the premises are assumed true, it is probable for the conclusions to be false.

In these arguments, the conclusion does not follow probably from the premises, even though it is claimed to.