Bibliography

Lowell Lectures on The Logic of Science; or Induction and Hypothesis: Lecture IX

By a ground, […] I meant the pure form or abstraction which is the original of the thing and of which the concrete thing is only an incarnation. Reference to such a ground or respect of likeness is implied in every attribution.

We come to […] the argument. [—] It will therefore be divided into three species according as this representation is a likeness, index, or symbol.

These three species are the same as Hypothesis, Induction, and Deduction. Hypothesis brings up to the mind an image of the true qualities of a thing - it therefore informs us as to comprehension but not as to Extension, that is it represents a representation which has Comprehension without Extension; in other words it represents a likeness.

An index represents its object by a real correspondence with it - as a tally does quarts of milk, and a vane the wind. [—] An index is a representation whose relation to its object is prescidible and is a Disquiparence, so that its peculiar Quality is not prescindible but is relative.

The reason why

is that Extension and Comprehension can only be reckoned by the interpretants, each interpretant measuring either the one or the other.

…by an interpretant we mean a representation which represents that something is a representation of something else of which it is itself a representation.

A likeness represents its object by agreeing with it in some particular. [—] Scientifically speaking, a likeness is a representation grounded in some internal character - that is whose reference to a ground is prescindible.

A symbol is a general representation like a word or conception. [—] A symbol is a representation whose essential Quality and Relation are both unprescindible - the Quality of being Imputed and the Relation ideal.