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I am studying a logic text book and there is the following example which I don't get:

Because I had decided, right off, that I liked John, what I heard in his answer was toughness and confidence.
Had I decided early on that I didn't like him, I would have heard in his reply arrogance and bluster.
The first impression becomes a self-fullfilling prophecy:we hear what we expect to hear

According to the book the first 2 propositions serves as premices for the 3rd which is the conclusion: i.e. we hear what we expect.

From my point of view though, the 3rd proposition could be a premise to conclude either of the first 2 propositions.

I.e. we hear what we expect to hear and therefore I heard in John's answer confidence since I liked him.

Am I wrong on this? Can't the 3rd proposition be a premise?
Why not? I don't follow

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Premises are whatever we state to be true without rigorous justification. They may be partially justified by obviousness, or completely unjustified but accepted as a thought experiment. In any case, within one particular argument, the premises are those things which are assumed to be true. Logic is then how we (validly) reason from those premises to a conclusion.

Given that many statements are statements of equality not just implication (e.g. a number is even (divisible by two) if and only if one plus that number is odd (not divisible by two)), one can often exchange certain premises for conclusions, and get a different set of premises and a different argument.

In the case of the passage in your book, however, this doesn't exactly seem to be the case. If the first two lines are taken to be premises, then the third one does not logically follow, except very weakly inductively, given that the first two are simply examples of one person's reactions (one of them hypothetical!) in one situation, and the "conclusion" is a universally quantified truism. Unless the universe consists of only that one encounter with John, this does not logically follow. You are correct that it works better the other way around: given the 3rd sentence as a premise, the 1st and 2nd are at least completely consistent (if not the only possible reactions that are logically consistent).

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    @ Rex Kerr:Thank you for the reply.Initially I thought that my observation might be wrong, and the point of the example was to show the use of Because as a premise indicator. Only in this way, as I can understand this example, can the 3rd sentence make sense as a conclusion. I am glad that my point of view is not erroneous – Jim Jan 2 '12 at 20:11
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I am studying a logic text book and there is the following example which I don't get

Which logic textbook is this? Because the example is drawn from Malcolm Gladwell, and I certainly wouldn't recommend using his writings as a source of rigorous (or even well-structured) syllogisms.

From my point of view though, the 3rd proposition could be a premise to conclude either of the first 2 propositions.

This is correct. A standard (deductive) syllogism moves from the general to the specific. In this case, the argument is structured inductively: that we should induce the general rule from the specific case.

If you are using this textbook for a course, I'd talk to your instructor. If you're studying on your own, I'd look for a better text.

  • This is from the book Introduction to Logic by Copi & Cohen.I am studying on my own. – Jim Jan 3 '12 at 17:44

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