Digital Companion to C. S. Peirce
1893 | Grand Logic 1893: Division III. Substantial Study of Logic Chapter VI. The Essence of Reasoning | CP 7.467

A concept is not a mere jumble of particulars, – that is only its crudest species. A concept is the living influence upon us of a diagram, or icon, with whose several parts are connected in thought an equal number of feelings or ideas. The law of mind is that feelings and ideas attach themselves in thought so as to form systems. But the icon is not always clearly apprehended. We may not know at all what it is; or we may have learned it by the observation of nature.

1894 | The Art of Reasoning. Chapter II. What is a Sign? | EP 2:10

We think only in signs. These mental signs are of mixed nature; the symbol-parts of them are called concepts. If a man makes a new symbol, it is by thoughts involving concepts. So it is only out of symbols that a new symbol can grow.

1904 [c.] | Draft of Nichols Review [C] | CP 8.191

The word pragmatism was invented to express a certain maxim of logic, which, as was shown at its first enouncement, involves a whole system of philosophy. The maxim is intended to furnish a method for the analysis of concepts. A concept is something having the mode of being of a general type which is, or may be made, the rational part of the purport of a word. A more precise or fuller definition cannot here be attempted.

1904 [c.] | Draft of Nichols Review [C] | MS [R] 1476:6

…when a philosopher speaks of the ‘concept’ of matter, or the ‘concept’ of cause, or any other ‘concept,’ what he means by a ‘concept’ is a word or other legisign.

1906 | The Basis of Pragmaticism | EP 2:387; LI 275

A concept is a symbol present to the imagination, – that is, more correctly speaking, of which a particular instance might be present to the imagination.

1907 | Pragmatism | MS [R] 318:44

Concepts are mental habits; habits formed by exercise of the imagination.

1907 [c.] | Prag [R] | MS [R] 322:9

A concept […] is a mental sign, and as such, is an intermediary whereby the object that it represents into some sort of correspondence with which it is moulded, can come to determine that effect, that meaning, which the sign itself is intended to awaken or otherwise determine.

nd | Fragments [R] | MS [R] 839

All signs are divided by the logicians into names, propositions, and argumentations. A mental name, or what one thinks when one thinks of the meaning of a name, is called a Concept.