Usual definitions of the transcendental are given by ontological assumptions. Typical in this regard are those in various theologies or philosophies. And needless to say, such ontological assumptions can easily be challenged, if not in fact, they actually do invite such challenges.
Plato’s Cave Allegory in his book ”Republic” is an exception, since it can be seen as a definition of the transcendental, albeit rather indirectly and through a quite involved story. And as such, it is not at all about any ontological assumption, but only about gnoseology, epistemology and pragmatics.
Here, a similar definition of the transcendental is suggested, namely, a definition which does not use any ontological assumption, and instead, it only refers to gnoseology, epistemology and pragmatics. The novelty is in the fact that the mentioned definition consists of nothing more than four successive questions.