Bibliography

Letter to J. H. Kehler

I have now sketched my doctrine of Logical Critic, skipping a good deal. I recognize two other parts of Logic. One which may be called Analytic examines the nature of thought, not psychologically but simply to define what it is to doubt, to believe, to learn, etc., and then to base critic on these definitions is my real method, though in this letter I have taken the third branch of logic, Methodeutic, which shows how to conduct an inquiry. This is what the greater part of my life has been devoted to, though I base it upon Critic.

…believing, real genuine belief, consists in a habit with which one is contented and which one usually recognizes (though not always)[,], this habit consisting in the general fact that under certain circumstances one would act in a definite way, and would be content to do so.

… my doctrine of Logical Critic [—] I recognize two other parts of Logic. One which may be called Analytic examines the nature of thought, not psychologically but simply to define what it is to doubt, to believe, to learn, etc., and then to base critic on these definitions is my real method, though in this letter I have taken the third branch of logic, Methodeutic, which shows how to conduct an inquiry. This is what the greater part of my life has been devoted to, though I base it upon Critic.

… An Induction can hardly be sound or at least is to be suspected usually, unless it has been preceded by a Retroductive reasoning to the same general effect. Induction chiefly serves to render more certain ideas that have already been otherwise suggested. I use “Induction” in a wider sense than usual. It is usually regarded as a reasoning by which one passes from asserting something of a number of single things to asserting the same of the whole class to which those things belong. I give the definition a somewhat different turn, at least, and throw much light upon Induction by defining it as any reasoning from a sample to the whole sampled.

… the third branch of logic, Methodeutic, which shows how to conduct an inquiry. This is what the greater part of my life has been devoted to, though I base it upon Critic.

I will venture to guess that you will be surprised to learn […] how true it is that a habit can be acquired by imaginary practice. Out of such considerations, which turn, as if upon a pivot, about the idea that a thought is nothing but a habit connected with a sign, one can build up quite a little philosophy which is what I meant by “pragmatism.”

I consider Retroduction (a poor name) to be the most important kind of reasoning, notwithstanding its very unreliable nature, because it is the only kind of reasoning that opens up new ground. [—] Retroduction gives hints that come straight from our dear and adorable Creator. We ought to labour to cultivate this Divine privilege. It is the side of human intellect that is exposed to influence from on high. With this investigation starts. Having once formed a conjecture, the first thing to be done is to draw Deductions from it and compare them with observations. [—]

So Retroduction comes first and is the least certain and least complex kind of Reasoning.

Skipping a great deal, I now take up the third great class of Reasonings, which I call Retroductions. [—] By the third class of reasonings one only infers that a certain state of things may be true and that the indications of its being so are sufficient to warrant further examination. [—] The reason for accepting the Retroductive conclusion, is that man must trust to his power of getting at the truth simply because it is all he has to guide him; and moreover when we look at the instincts of various animals, we are struck with wonder at how they lead those creatures toward rational behaviour. [—]

I do not, at present, feel quite convinced that any logical form can be assigned that will cover all “Retroductions”. For what I mean by a Retroduction is simply a conjecture which arises in the mind.

I am unable yet quite to prove that the three kinds of reasoning I mean are the only kinds of sound reasoning; though I can show reason to think that it can be proved, and very strong probable reasons for thinking that there is no fourth kind. I call the three, Deduction, Induction, and Retroduction; though the last only is a word invented by me.

A scientific inquiry must usually, if not always, begin with retroduction. An Induction can hardly be sound or at least is to be suspected usually, unless it has been preceded by a Retroductive reasoning to the same general effect.