"I hold that the mark of a genuine idea is that its possibility can be proved, either a priori by conceiving its cause or reason, or a posteriori when experience teaches us that it is in fact in nature"

The quote by Gottfried Leibniz suggests that a real or authentic concept is one that can be proven to be possible. It can either be proven through logical reasoning (a priori) by comprehending its cause or reason or through practical experience (a posteriori) where it can be observed to exist naturally. The author highlights the value of sound thinking and proof in developing the credibility of a concept.