It is only man’s consciousness, a consciousness capable of conceptual errors,
that needs a special identification of the directly given, to embrace and
delimit the entire field of its awareness—to delimit it from the void of
unreality to which conceptual errors can lead. Axiomatic concepts are
epistemological guidelines. They sum up the essence of all human cognition:
something exists of which I am conscious; I must discover its identity.
Since axiomatic concepts are identifications of irreducible primaries, the only
way to define one is by means of an ostensive definition—e.g., to define
“existence,” one would have to sweep one’s arm around and say: “I mean this.”