Logic is the art of reasoning well. It is also a science, the science of second intentions, that is, of the relations things have only as they are known, such as genus, species, subject, predicate, statement, and conclusion. Logic studies words in so far as they signify things through our thoughts, and it orders our discourse toward truth.
The three acts of the mind
The tradition distinguishes three acts of the mind, and logic studies each in turn.
- Simple apprehension grasps what something is. What it forms is a term, and its aim is a definition.
- Judgment joins or separates terms, affirming or denying one thing of another. What it forms is a proposition, which is true or false.
- Reasoning moves from propositions we know to a proposition we did not know. What it forms is an argument, which either follows or does not.
| Act of the mind | What is formed | What is at stake |
|---|---|---|
| Apprehension | Term, definition | What is meant |
| Judgment | Proposition | True or false |
| Reasoning | Argument | Whether it follows |
Truth first becomes possible in the second act. A term such as “man” or “white” signifies but is neither true nor false. So the first act aims at definition rather than truth, and someone who tries to argue before he can define is trying to perform the third act without the first two.
Opposition, inference, and fallacy
In the second act we also learn how propositions relate to one another. Two propositions may contradict each other, so that one must be true and the other false; or they may be contraries, which cannot both be true but may both be false. In the third act, two propositions that share a middle term lead to a conclusion; this is the syllogism. These are only some examples from the study of the acts of the mind.
Not everything that looks like reasoning is reasoning. Conway defines a fallacy as reasoning that appears to conclude but does not (Aristotelian Formal and Material Logic, ch. 1), and he notes that the most dangerous fallacies are the ones that do not appear to be fallacies.
Formal and material logic
Formal logic studies the structure of the three acts. Material logic asks how certain a conclusion is, given what its premises are about: demonstration gives a necessary conclusion, dialectical argument gives a probable one, rhetoric moves to one side of a question or the other, and sophistry gives only the appearance of proof or probability (Houser, Logic as a Liberal Art). Because these forms are already present in the language we speak, this course begins from language rather than from symbolic logic, which has its uses but is not the first form of the art.
Logic and rhetoric
A conclusion can follow necessarily from true premises and still fail to persuade an audience; and a speech can persuade a hearer without having shown anything. Logic considers truth, and rhetoric considers the means of persuading others of a truth.
Continue to Studying Logic.