CONDITIONS OF IMMEDIATE INFERENCE

Sec. 1.  The word Inference is used in two different senses, which are often confused but should be carefully distinguished.  In the first sense, it means a process of thought or reasoning by which the mind passes from facts or statements presented, to some opinion or expectation.  The data may be very vague and slight, prompting no more than a guess or surmise; as when we look up at the sky and form some expectation about the weather, or from the trick of a man’s face entertain some prejudice as to his character.  Or the data may be important and strongly significant, like the footprint that frightened Crusoe into thinking of cannibals, or as when news of war makes the city expect that Consols will fall.  These are examples of the act of inferring, or of inference as a process; and with inference in this sense Logic has nothing to do; it belongs to Psychology to explain how it is that our minds pass from one perception or thought to another thought, and how we come to conjecture, conclude and believe (cf. chap. i.  Sec. 6).

In the second sense, ‘inference’ means not this process of guessing or opining, but the result of it; the surmise, opinion, or belief when formed; in a word, the conclusion:  and it is in this sense that Inference is treated of in Logic.  The subject-matter of Logic is an inference, judgment or conclusion concerning facts, embodied in a proposition, which is to be examined in relation to the evidence that may be adduced for it, in order to determine whether, or how far, the evidence amounts to proof.  Logic is the science of Reasoning in the sense in which ‘reasoning’ means giving reasons, for it shows what sort of reasons are good.  Whilst Psychology explains how the mind goes forward from data to conclusions, Logic takes a conclusion and goes back to the data, inquiring whether those data, together with any other evidence (facts or principles) that can be collected, are of a nature to warrant the conclusion.  If we think that the night will be stormy, that John Doe is of an amiable disposition, that water expands in freezing, or that one means to national prosperity is popular education, and wish to know whether we have evidence sufficient to justify us in holding these opinions, Logic can tell us what form the evidence should assume in order to be conclusive.  What form the evidence should assume:  Logic cannot tell us what kinds of fact are proper evidence in any of these cases; that is a question for the man of special experience in life, or in science, or in business.  But whatever facts constitute the evidence, they must, in order to prove the point, admit of being stated in conformity with certain principles or conditions; and of these principles or conditions Logic is the science.  It deals, then, not with the subjective process of inferring, but with the objective grounds that justify or discredit the inference.