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bu means of it of the constitutions of different reasonings, and practice with it, helps immensely to make thought clearer, and thus is indirectly condusive to skill in reasoning.

The system of expression which I am going to describe is a system of diagrams; and these diagrams I call existential graphs. - Insert opposite as over page.
Everything we call a diagram appeals to the eye; and yet at the same time involves conventional signs.
This system involves 14 conventions, or agreements that you and I shall have to come to as to the significations of parts of our graphs.
To these fourteen I may prefix one which I will call Convention O since it does not pertain to this particular system but to every system of convention of whatever beind Convention O.
Whatever feature of the signs is not the subject of an express convention can be freely varied without influence in the use.

To begin, with every act of expression or of representation supposes two persons, one who makes the signs and another who interprets