IDENTIFYING THE LOGIC OF AN ARGUMENT

Bob Corbett

PHIL 1010 01: June 5th until July 28th, 2000

The Logic: Class lecture

I will begin this lecture with a surprise: The smallest unit of discourse in critical thinking is the argument and the argument has two parts -- the thesis and the set of reasons and considerations for the thesis.. Never heard that before, have you.

These very brief notes here are to introduce the notion of the LOGIC of an argument.

The logic of an argument concerns the CONNECTION between the thesis and the set of reasons and considerations. The reasons and considerations must be CONNECTED to the thesis such that if the reasons and considerations are accurate and persuasive, then we are driven forcefully to accept the thesis. The reasons and considerations are LOGICALLY connected to the thesis, that is, they suggest strongly that if they are reliable, then the thesis must follow.

I am not going to delve very deeply into logic in this short essay, nor in this short course. I will say a few things for information, but the main issue is just what is said in the paragraph above and understanding what it means.

I do want to introduce a different language to discuss the logic. What I am calling the thesis and set of reasons and considerations have different names when we speak of the logic. These are:

thesis = CONCLUSION. That is to say, the thesis follows from the reasons and considerations, and thus is the conclusion of thinking about them and what they mean. Conclusion is one of the synonyms I earlier introduced for thesis.

the set of reasons and considerations = PREMISES. That is to say, given that an argument is an

IF ----- THEN

structure, the premises are the IF part. IF they are true, then, if they are also connected logically to the THEN (conclusion--thesis) part of the argument, then the argument is seen as reliable.

Logic comes in at least two broad forms. One is sort of logic "proper" and it maintains something stronger than I am suggesting. Logic proper concerns a NECESSARY connection between the conclusion (thesis) and the premises (set of reasons and considerations). It holds that if there is a strictly formal relationship between the two (premises and conclusion), then it is impossible for the premises to be true and the conclusion not be.

Here is an easy example:

If (premise 1) All unmarried men a bachelors.
and
if (premise 2) John is unmarried.

then (conclusion) John is a bachelor.

This is seen as a necessary connection between the premises and the conclusion.

However, in the more loose form of critical thinking which I am introducing, MOST arguments will not actually have this formal sense of logic in the connection between premises and conclusion. The connection will be much more informal. We will just have to "see" in some intellectual sense, that the premises are logically connected to the premises. We will pick up some tools for criticizing the logic of an argument, even in this informal sense, later on when we get to evaluation or criticism.

We do need a central term here:

Arguments (premises and conclusion) are said to be connected logically and a decent argument, one in which that connection is actually there, is said to be a SOUND argument.
An argument (premises and conclusion) in which that logical connection is not present is said to be an UNSOUND argument.

Thus arguments are not TRUE or VALID as they are sometimes called, but SOUND or UNSOUND.

This is just a piece of technical jargon, but you do need to learn it and use it. To say that an argument is SOUND is to tell us NOTHING about the truth or reliability of either the premises or conclusion (it tells us nothing about the truth or reliability of the thesis or set of reasons and considerations). Rather, the soundness or unsoundness of an argument tells us about the CONNECTION between the premises and conclusion, such that we can know that WERE the premises true or reliable, then the conclusion would indeed follow.

Again, some very useful vocabulary in thinking about arguments:

1. An argument in which there is a reasonable CONNECTION between a set of premises and a conclusion is said to be a SOUND argument. We learn nothing about the TRUTH or RELIABLITY of the conclusion from soundness alone.
2. On the other hand, if an argument is SOUND, and the premises are TRUE or RELIABLE, then we can trust that the conclusion is also TRUE or RELIABLE.
3. However, note, importantly, that if the premises are as true and true as can be, or as reliable and reliable as can be, but the argument is logically UNSOUND, then we know absolutely nothing about the conclusion. It is not known to be EITHER true and reliable or false and unreliable. If the argument is logically UNSOUND, then there is no connection of any kind whatsoever between the premises and conclusion, so no judgment can be rendered about the conclusion (thesis).

Conclusions (theses) cannot be true or false, reliable or unreliable APART from the argument itself. Recall, the smallest unit of sense in critical thinking is the argument, not the thesis alone. Only sound arguments can have true or reliable conclusions, but not ALL sound arguments have true or reliable conclusions, only the sound arguments whose premises are also themselves true or reliable.

This is extremely short and highly abstract. Ask all the questions you need to get this clearer in your head.

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Bob Corbett corbetre@webster.edu