Documents

What is an Argument

Categories
Published
of 3
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Description
Basic structure of a logical argument
Transcript
  WHAT IS AN ARGUMENT?An argument is defined as a list of claims, all but the last of which are labelled premises, the last of which is labelled a conclusion.A 'good' argument has three features:1) Validity;2) Soundness;3) Potential Convincingness.VALIDITYAn argument is valid when it is impossible that its premises be true and its conclusion false.The following is an example of a valid argument.Premise 1: I have a watch in one of my two pockets.Premise 2: My right pocket is empty.Conclusion: I have a watch in my left pocket.There is no possible situation in which both premises are true and the conclusion is false.The following is an example of an invalid argument.Premise 1: I have a watch in one of my two pockets.Premise 2: In my right pocket I have a wallet.Conclusion: I have a watch in my left pocket.There is at least one situation in which both premises can be true, but the conclusion is false. For example, both wallet and watch are in my right pocket. In general, in order to show that an argument is invalid identify a possible situation in which its premises are true, but the conclusion is false.An argument may have true premises and a true conclusion, but still be invalid as the following example shows.Premise 1: MIT is located in the USA.Premise 2: MIT is located in Massachusetts.Conclusion: MIT is located in Cambrdige.It could have been that both premises were true and the conclusion false. MIT could have been located in, for example, Boston.An argument may have true premises and a false conclusion, but still be valid as the following example shows.Premise 1: If an object is Yellow, then it is made of cheese.Premise 2: My car is yellow.  Conclusion: My car is made of cheese.This is a valid argument since there is no possible situation in which both premises are true and the conclusion false. But its conclusion is false. (Notice that Premise 1 is false, too. This is not a coincidence. If a valid argument has a false conclusion then at least one of its premises must be false.)Simpson's ParadoxConsider the following argument.Premise 1: Damien and Ryan have taken Art and Math classes, and only Art and Math classes.Premise 2: Damien's mean grade in Art is higher than Ryan's.Premise 3: Damien's mean grade in Math is higher than Ryan's.Conclusion: Damien's mean overall grade is higher than Ryan's.Intuitively, this seems a valid argument. However, it is possible for Ryan's overall mean grade to be higher than Damien's even though Damien's mean grade in Math and mean grade in Art are both higher than Ryan's. Suppose Damien took one Math class, in which he got an A, and three Art classes, in which he got Cs. Ryan, meanwhile, took three Math classes, in which he got As, and one Art class, in which he got a C.This is a possible situation in which Damien has better average grades than Ryan in both Math and Art, but Ryan has a better average overall. So it is possible for the premises of the argument to be true and its conclusion false. Therefore, the argument is invalid.This is an example of Simpson's paradox, a paradox in which a trend that appears in different groups of data disappears when these groups are combined, and the reverse trend appears for the aggregate data.SOUNDNESSAn argument is sound when it is valid and its premises are true.A sound argument always has a true conclusion. If the premsises are true (soundness), and its impossible that the premises are true and the conclusion is false (validity), then the conclusion must be true.Consider the following argument.Premise 1: All politicians are honest.Premise 2: Senator Warren is a politician.Conclusion: Senator Warren is honest.This argument is valid because it is impossible for all its premises to be true and its conclusion false. But it is unsound because its first premise is false.Consider the following argument.Premise 1: All politicians do politics.  Premise 2: Senator Warren is a politician.Conclusion: Senator Warren does politics.The argument is sound because it is valid and all its premises are true. It is true that all politicians should be honest, and it is true that Elizabeth Warren is a politician (she is a Senator from Massachusetts).Finally consider the following argument.Premise 1: All humans are mortal.Premise 2: Socrates is mortal.Conclusion: Socrates is a human.This argument has all true premises but it it is invalid (Socrates may be a different animal, e.g. a dog). So it is not sound.POTENTIAL CONVINCINGNESSAn argument is potentially convincing for a person when, prior to being confronted with the argument, the person believes the premises but does not believe the conclusion, and the person is in a position to see that the argument is valid.A person who finds an argument to be potentially convincing will be more inclined to accept the conclusion since they already find the premises convincing and can see that the argument itself is valid.Consider the following argument.Premise 2: God exists.Conclusion: God exists.This is not as potentially convincing argument because nobody who would believe the premise prior to being confronted with the argument would not believe the conclusion.Another argument that is not potentially convincing is the following.Premise 1: Everything written in the Bible is true.Premise 2: It is written in the Bible that God exists.Conclusion: God exists.Anyobody that would accept the first premise as true would also believe that God must exist, therefore would beleive the conclusion prior to being confronted with the argument.

Anyway

Jul 23, 2017
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks