Digital Companion to C. S. Peirce
1895-6 [c.] | That Categorical and Hypothetical Propositions are one in essence, with some connected matters | CP 2.339

Every subject, when it is directly indicated, as humanity and mortality are, is singular. Otherwise, a precept, which may be called its quantifier, prescribes how it is to be chosen out of a collection, called its universe. In probable logic, the quantifiers – such as “nine out of ten,” and the like – refer to an experiential course or “long run.” But in necessary logic there is no reference to such a course of experience, and only two quantifiers are required; the universal quantifier, which allows any object, no matter what, to be chosen from the universe, and the particular quantifier, which prescribes that a suitable object must be chosen. When there are several quantified subjects, and when quantifications are different, the order in which they are chosen is material. It is the character of the quantifier of the last chosen subject which extends itself to the whole proposition.

1902 | Subject (in logic) | CP 2.357

When the subject is not a proper name, or other designation of an individual within the experience (proximate or remote) of both speaker and auditor, the place of such designation is taken by a virtual precept stating how the hearer is to proceed in order to find an object to which the proposition is intended to refer. If this process does not involve a regular course of experimentation, all cases may be reduced to two with their complications. These are the two cases: first, that in which the auditor is to take any object of a given description, and it is left to him to take any one he likes; and, secondly, the case in which it is stated that a suitable object can be found within a certain range of experience, or among the existent individuals of a certain class.

1903 | Syllabus: Syllabus of a course of Lectures at the Lowell Institute beginning 1903, Nov. 23. On Some Topics of Logic | CP 2.330; EP 2:286

Every subject of a proposition, unless it is either an Index (like the environment of the interlocutors, or something attracting attention in that environment, as the pointing finger of the speaker) or a Sub-index (like a proper name, personal pronoun or demonstrative) must be a Precept, or Symbol, not only describing to the Interpreter what is to be done, by him or others or both, in order to obtain an Index of an individual (whether a unit or a single set of units) of which the proposition is represented as meant to be true, but also assigning a designation to that individual, or, if it is a set, to each single unit of the set. Until a better designation is found, such a term may be called a Precept.