unascertainable

adj

1. That cannot be ascertained; uncertain, unable to be determined or discovered.

   “Everything one would wish to know of the relations of Aristotle and Alexander is unascertainable, the more so as legends were soon invented on the subject.”

   “Reality is different from, and more than, the totality of facts and events, which, anyhow, is unascertainable.”

   “The regulation's vagueness is especially apparent in the last clause quoted above. That portion of the test is expressly based on an individualistic—and therefore necessarily varying and unascertainable—standard: the reactions of members of the public.”