A graph is the propositional expression in the System of Existential Graphs of any possible state of the universe. It is a Symbol, and, as such, general, and is accordingly to be distinguished from a graph-replica. A graph remains such though not actually asserted. An expression, according to the conventions of this system, of an impossible state of things (conflicting with what is taken for granted at the outset or has been asserted by the graphist) is not a graph, but is termed The pseudograph, all such expressions being equivalent in their absurdity.

A pseudograph is a construction out of elements like those of graphs, but which, owing to the way in which these are put together, has no meaning as a diagram of the system to which it belongs.

The assertion of that which is unintelligible (i.e. absurd) not being a graph shall be called the pseudograph, and may be represented by filling the entire area in which it is, so as to leave room for nothing else.