Ancient Greek was capable of discerning between several different forms of knowing. These different forms may be described in English as being propositional knowledge, indicative of knowledge acquired indirectly through the reports of others or otherwise by inference (such as "I know of George Bush" or "I know Berlin is in Germany"), and empirical knowledge acquired by direct participation or acquaintance (such as "I know George Bush personally" or "I know Berlin, having visited").

Gnosis (γνῶσις) refers to knowledge of the second kind. Therefore, in a religious context, to be "Gnostic" should be understood as being reliant not on knowledge in a general sense, but as being specially receptive to mystical or esoteric experiences of direct participation with the divine. Indeed, in most Gnostic systems the sufficient cause of salvation is this "knowledge of" ("acquaintance with") the divine. This is commonly identified with a process of inward "knowing" or self-exploration, comparable to that encouraged by Plotinus (c. 205 – 270 AD). This is what helps separate Gnosticism from proto-orthodox views, where the orthodox views are considered to be superficial.