Published on *Commens* (http://www.commens.org)

Line of Identity

1903 | A Syllabus of Certain Topics of Logic | Peirce, 1903, p. 22; CP 4.416

The *line of identity* is a Graph any replica of which, also called a line of identity, is a heavy line with two ends and without other topical singularity (such as a point of branching or a node), not in contact with any other sign except at its extremities. Otherwise, its shape and length are matters of indifference. All lines of identity are replicas of the same graph.

1903 | A Syllabus of Certain Topics of Logic | Peirce, 1903, p. 18; CP 4.406

A heavily marked line without any sort of interruption (though its extremity may coincide with a point otherwise marked) shall, under the name of a *line of identity*, be a graph, subject to all the conventions relating to graphs, and asserting precisely the identity of the individuals denoted by its extremities.

1903 | Graphs, Little Account [R] | MS [R] S27:22

A heavily marked continuous line on the sheet of assertion shall assert that the individuals denoted by its two extremities are identical. [—]

Such a line is called a *line of identity*.

1903-09-15 | Existential Graphs | MS [R] S28:47

A heavily marked uninterrupted line on the sheet of assertion, having two extremities and no branching shall be called a *line of identity* and shall be a graph asserting the identity of all the individuals denoted by its points (all which being heavily marked denote individuals).