Being Logical: A Guide to Good Thinking

by D.Q. McInerny

Argument: The Language of Logic

The concrete expression of logical reasoning is the argument. An argument stands or falls to the extent that the reasoning it incorporates is good or bad.

Every argument is composed of two basic elements, two different types of statements: a “premise” statement and a “conclusion” statement.

Common logical indicators for premises are “because,” “since,” “on account of.” Common logical indicators for conclusions are “therefore,” “thus,” “so.”

More elaborate expressions can be used to announce premises (“in view of the fact that,” etc.) and conclusions (“it necessarily follows that,” etc.).

The nature of a universal statement is such that, if it is true, a particular statement with the same subject and predicate is also true.

Knowledge of a part does not allow me to say anything definitive about the whole.

The whole can contain a part, but a part cannot contain the whole.

“Affirmative statements” connect ideas; “negative statements” disconnect ideas.

if the same idea can be communicated both affirmatively and negatively, it is better to opt for the affirmative construction.

The affirmative statement is more direct and emphatic. (This is true of all affirmative statements.) Because its emphasis is on what is the case rather than on what is not the case, it elicits a positive response. The negative statement, by emphasizing what is not the case, prompts us to think in negative terms about the situation being described.

sense. Seldom is it the case that there is a real necessary connection between antecedent and consequent in our arguments. The result of this is that the conclusions we reach in our arguments do not necessarily follow. This does not mean, however, that conditional argument that yields anything less than necessary conclusions is of no value, much less that it is irresponsible to use such argument.

Our aim should be to construct our arguments in such a way that their conclusions will carry as high a degree of probability as possible.

The syllogism is a form of argument that reflects the way the human mind habitually operates: that is, connecting ideas in such a way that conclusions can be drawn from those connections.

In constructing an argument, the first thing to be mindful of is the two basic elements of argument: premises and a conclusion. You will not end up with an argument if you simply make statements. Your statements must be such that some of them (the premises) serve as the supporting data for another statement (the conclusion). Focus your attention on the premises.

Selective skepticism is merely a matter of reserving judgment until we have sufficient information at hand to judge responsibly.

But skepticism as a permanent attitude, a philosophical point of view, is deadly. It subverts the reasoning process before it even gets started, transforming it into a process of mis-reasoning.

Logic, though more than common sense, is born out of it. Success in logical thinking, then, and in the avoidance of illogical thinking, is rooted in a respect for common sense.

Rule of thumb: Make as few assumptions as possible.

The mere fact that “things have always been done that way” is not in and of itself a compelling reason for keeping on doing them that way. It all depends on what is actually being done. Habit is a powerful influence in our lives, and we can become habituated to ways of doing things that are not intrinsically worthwhile. In evaluating a given practice, we have to keep our attention focused on the practice, not on its history.

But there is an opposite kind of mistake we can make with respect to tradition. If it is illogical to single out the longevity of a practice as the sole reason for continuing it, it is just as illogical to cite the practice’s longevity as the sole reason for abandoning it. The attitude behind this mistake is a certain type of modernist thinking which assumes that only the new is worthwhile and that the only permanency we should commit ourselves to is the permanency of change.

A practice is not necessarily a bad practice because it has a history behind it. Indeed, it is conceivable that the best explanation for...

To repeat an important rule: In argumentation we respond to the argument, not to the person behind the argument. That rule is broken when the argument is ignored and the person responsible for the argument is deliberately attacked.

When that happens the “ad hominem fallacy” is being committed. (Ad hominem, in Latin, means “against the person.”)

If my only purpose is to win an argument, the ad hominem fallacy can effectively advance that cause.

In the aftermath I might congratulate myself that I won the argument, but that is precisely what I did not do—not in any logical sense, at any rate. My dubious victory was not based on the merits of my ideas, but on my ability to prevent the argument of my opponent from getting a fair hearing.

Because we are by nature analytic creatures, we have to take things apart, mentally if not physically, in order fully to understand them. But analysis is only productive if it is complemented by synthesis. It is not enough to take things apart; we have to put them back together again.

Important though it is to avoid the pitfalls of poor reasoning, it is more important to concentrate our energies on mastering those positive principles that make for its happy opposite—sound reasoning. And this is where practice comes in. Logic can be perfected as an art only by our putting it to work, by regularly applying it to real-life situations. We could never complain of a lack of opportunities for doing this; all our waking hours are chock-full of situations that demand logical responses from us.