H. P. Grice: The Philosopher's Boot Strap

"I once invented (though I did not establish its validity) a principle which I labelled as “Boot Strap."

“The Boot Strap principle lays down that, when one is introducing the primitive concept of a theory Th formulated in the object-language L1, the philosopher has freedom to use a concept C1 expressible in the meta-language L2, subject to the condition that a counterpart C2 of such a concept C1 is sub-sequently definable or otherwise derivable in the object-language L1.”

“So the more economically the philosopher introduces the ‘primitive’ object-language L1 concept C1, the less of a task the philosopher leaves himself for the morrow.”