Digital Companion to C. S. Peirce
1878 | How to Make Our Ideas Clear | W 3:262-3; ILS 86; CP 5.395

These two sorts of objects, what we are immediately conscious of and what we are mediately conscious of, are found in all consciousness. Some elements (the sensations) are completely present at every instant so long as they last, while others (like thought) are actions having beginning, middle, and end, and consist in a congruence in the succession of sensations which flow through the mind. They cannot be immediately present to us, but must cover some portion of the past or future. Thought is a thread of melody running through the succession of our sensations.

1880 | On the Algebra of Logic | W 4:164; CP 3.160

A cerebral habit of the highest kind, which will determine what we do in fancy as well as what we do in action, is called a belief. The representation to ourselves that we have a specified habit of this kind is called a judgment. A belief-habit in its development begins by being vague, special, and meagre; it becomes more precise, general, and full, without limit. The process of this development, so far as it takes place in the imagination, is called thought.

1885 | One, Two, Three: Fundamental Categories of Thought and of Nature | CP 1.377

It seems, then, that the true categories of consciousness are: first, feeling, the consciousness which can be included with an instant of time, passive consciousness of quality, without recognition or analysis; second, consciousness of an interruption into the field of consciousness, sense of resistance, of an external fact, of another something; third, synthetic consciousness, binding time together, sense of learning, thought.

1902 | Minute Logic: Chapter II. Prelogical Notions. Section I. Classification of the Sciences (Logic II) | CP 7.364

… the psychologists undertake to locate various mental powers in the brain; and above all consider it as quite certain that the faculty of language resides in a certain lobe; but I believe it comes decidedly nearer the truth (though not really true) that language resides in the tongue. In my opinion it is much more true that the thoughts of a living writer are in any printed copy of his book than that they are in his brain.

1903 | Syllabus: Syllabus of a course of Lectures at the Lowell Institute beginning 1903, Nov. 23. On Some Topics of Logic | EP 2:272

In the ideas of Firstness, Secondness, and Thirdness, the three elements, or Universal Categories, appear under their forms of Firstness. They appear under their forms of Secondness in the ideas of Facts of Firstness, or Qualia, Facts of Secondness, or Relations, and Facts of Thirdness, or Signs; and under their forms of Thirdness in the ideas of Signs of Firstness, or Feeling, i.e., things of beauty; Signs of Secondness, or Action, i.e., modes of conduct; and Signs of Thirdness, or Thought, i.e., forms of thought.

1903 | Syllabus: Syllabus of a course of Lectures at the Lowell Institute beginning 1903, Nov. 23. On Some Topics of Logic | EP 2:269

Thirdness is found wherever one thing brings about a Secondness between two things. In all such cases, it will be found that Thought plays a part. By thought is meant something like the meaning of a word, which may be “embodied in,” that is, may govern, this or that, but is not confined to any existent. Thought is often supposed to be something in consciousness; but on the contrary, it is impossible ever actually to be directly conscious of thought. It is something to which consciousness will conform, as a writing may conform to it. Thought is rather of the nature of a habit, which determines the suchness of that which may come into existence, when it does come into existence. Of such a habit one may be conscious of a symptom; but to speak of being directly conscious of a habit, as such, is nonsense. In a still fuller sense, Thirdness consists in the formation of a habit.

1904 [c.] | Topical Geometry | MS [R] 137:18-9

What we call a “thought,” not that which is in somebody’s mind at one moment, and is gone, but that which passes from mind to mind, say the idea of Justice, is certainly of the nature of a word. People think it is of no consequence because it needs to be embodied in a passing thought or in the habit of some person before it can be effective. That undoubtedly is true. But the image in the mind would be of no consequence if it were not governed by or conformed to the thought. The two factors are both indispensible. But the difference is, that given the word, it matters comparatively little whether it is embodied in this momentary thought or in that; the effect will be substantially the same. But it makes a good deal more difference whether the image in the mind be joined by its associations with this concept or with that.

1905 | Notes on Portions of Hume's "Treatise on Human Nature" | MS [R] 939:25-6

Our thought is in my opinion […] an appeal in symbols of the self of the present to the self of the immediate future. It is conducted, if not in propositions, in something very much of that nature. I do not think it is, in its movement, propositional; but we are continually drawing up propositions or “judgments” to formulate it. The propositions are an interpretation of the thought, and the thought is partly an interpretation of the percept.

1906 [c.] | On Existential Graphs as an Instrument of Logical Research | MS [R] 498

…it is necessary to draw a distinction between thinking and thought. A sentence printed in a book is true or false. It embodies thought, although it does no thinking. [—]

…all deliberative meditation, or thinking proper, takes the form of a dialogue. The person divides himself into two parties which endeavour to persuade each other. From this and sundry other strong reasons, it appears that all cognitive thought is of the nature of a sign or communication from an uttering mind to an interpreting mind.

1906 [c.] | On the System of Existential Graphs Considered as an Instrument for the Investigation of Logic | MS [R] 499(s)

Do not confound thought with thinking. Thought is the Object that you think. Thinking, as contradistinguished from feeling and from the effort of attention, is the operation of the mind by which you strive to make out the Truth. You expect to extract it from the object before your mind, the Thought. That thought, then, is (or you hope it may be) a Sign of the Truth. Thought then is a Sign.

1906-7 | PAP [ed.] | MS [R] 293:5-6; NEM 4:314

‘Thinking’ is a fabled ‘operation of the mind’ by which an imaginary object is brought before one’s gaze. If that object is a Sign upon which an argument may turn, we call it a Thought. All that we know of the ‘Thinking’ is that we afterwards remember that our attention was actively on the stretch, and that we seemed to be creating Objects or transformations of Objects while noting their analogy to something supposed to be real. We choose to call ‘an operation of the mind’; and we are, of course, quite justified in doing so, provided it be well understood that its being so consists merely in our so regarding it, just as Alexander, Hannibal, Caesar, and Napoleon constitute a single quaternion, or plural of four, as long as we put them together in thought. The ‘operation of the mind’ is an ens rationis. That is my insufficient excuse for speaking of it as ‘fabled’.

1907 | Pragmatism | EP 2:428-9; MS [R] 318:39

…thoughts ought to be regarded as signs. Let anybody call to mind some recent earnest self-deliberation, and I think he will acknowledge that it took a dialogic form, every reasoning appealing to the self of the near following moment of time for assent and confirmation.

1909 | Meaning Preface | MS [R] 637:28

True Thought takes the form […] of a dialogue. For true thought is deliberate, and deliberation implies the asking of questions, and appeals to another personality for confirmation, objections, and other dialogic forms.