"When it happens that a new belief comes to one as consciously generated from a previous belief, - an event which can only occur in consequence of some third belief (stored away in some dark closet of the mind, as a habit of thought) being in a suitable relation to that second one, - I call the event and inference, or a reasoning." ('An Essay toward Improving Our Reasoning in Security and in Uberty', EP 2:463, 1913)

"Reasoning-power; or Ratiocination, called by some Dianoetic Reason, is the power of drawing inferences that tend toward the truth, when their premises or the virtual assertions from which they set out are true." (''An Essay toward Improving Our Reasoning in Security and in Uberty', EP 2:464, 1913)

"By "Reasoning" shall here be meant any change in thought that results in an appeal for some measure and kind of assent to the truth of a proposition called the "Conclusion" of the reasoning, as being rendered "Reasonable" by an already existing cognition (usually complex) whose propositional formulation shall be termed the "Copulate Premiss" of the reasoning. The reader will remark, as the point where this definition most markedly breaks with actual usage, that it refuses the name of reasoning to the synthesis into one recognition of the major and minor premises of a syllogism." (' A Sketch of Logical Critics', EP 2: 454, 1911)

"… For this theory requires that in reasoning we should be conscious, not only of the conclusion, and of our deliberate approval of it, but also of its being the result of the premises from which it does result, and furthermore that the inference is one of a possible class of inferences which conform to one guiding principle. Now in fact we find a well-marked class of mental operations, clearly of a different nature from any others which do possess just these properties. They alone deserve to be called reasonings; and if the reasoner is conscious, even vaguely, of what his guiding principle is, his reasoning should be called a logical argumentation." ('Issues of Pragmaticism', EP 2: 348, 1905)

"Reasoning is the process by which we attain a belief which we regard as the result of previous knowledge. [---]
      Again, a given belief may be regarded as the effect of another given belief, without our seeming to see clearly why or how. Such a process is usually called an inference; but it ought not to be called a rational inference, or reasoning. A blind force constrains us. [---] The word illation signifies a process of inference. Reasoning, in general, is sometimes called ratiocination. Argumentation is the expression of a reasoning." ('Short Logic', EP 2: 11-12, 1895)