5.3.2 The Difference between Truth and Logic

Analysis of arguments ought to take place on the levels of both truth and logic. Truth analysis is the determination of whether statements are correct or accurate. On the other hand, logical analysis ascertains whether the premises of an argument support the conclusion.

Often, people focus solely on the truth of an argument, but in philosophy logical analysis is often treated as primary. One reason for this focus is that philosophy deals with subjects in which it is difficult to determine the truth: the nature of reality, the existence of God, or the demands of morality. Philosophers use logic and inference to get closer to the truth on these subjects, and they assume that an inconsistency in a position is evidence against its truth.

Logical Analysis

Because logic is the study of reasoning, logical analysis involves assessing reasoning. Sometimes an argument with a false conclusion uses good reasoning. Similarly, arguments with true conclusions can use terrible reasoning. Consider the following absurd argument:

1. The battle of Hastings occurred in 1066.
2. Tamaracks are deciduous conifer trees.
3. Therefore, Paris is the capital of France.

The premises of the above argument are true, as is the conclusion. However, the argument is illogical because the premises do not support the conclusion. Indeed, the premises are unrelated to each other and to the conclusion. More specifically, the argument does not contain a clear inference or evidence of reasoning. An inference is a reasoning process that leads from one idea to another, through which we formulate conclusions. So in an argument, an inference is the movement from the premises to the conclusion, where the former provide support for the latter. The above argument does not contain a clear inference because it is uncertain how we are supposed to cognitively move from the premises to the conclusion. Neither the truth nor the falsity of the premises helps us reason toward the truth of the conclusion. Here is another absurd argument:

1. If the moon is made of cheese, then mice vacation there.
2. The moon is made of cheese.
3. Therefore, mice vacation on the moon.

The premises of the above argument are false, as is the conclusion. However, the argument has strong reasoning because it contains a good inference. If the premises are true, then the conclusion does follow. Indeed, the argument uses a particular kind of inference—deductive inference—and good a deductive inference guarantees the truth of its conclusion as long as its premises are true.

The important thing to remember is that a good inference involves clear steps by which we can move from premise to premise to reach a conclusion. The basic method for testing the two common types of inferences—deductive and inductive—is to provisionally assume that their premises are true. Assuming a neutral stance in considering an inference is crucial to doing philosophy. You begin by assuming that the premises are true and then ask whether the conclusion logically follows, given the truth of those premises.

Truth Analysis

If the logic in an argument seems good, you next turn to assessing the truth of the premises. If you disagree with the conclusion or think it untrue, you must look for weaknesses (untruths) in the premises. If the evidence is empirical, check the facts. If the evidence is a principle, ask whether there are exceptions to the principle. If the evidence is a conceptual claim, think critically about whether the conceptual claim can be true, which often involves thinking critically about possible counterexamples to the claim.