- Proceeding from a known or assumed cause to a necessarily related effect; deductive. Made before or without examination; not supported by factual study.

“In any investigation of the constitutional powers of these great Dominion legislatures, it is not proper that a Court should deny to such a legislature the right of solving taxation problems unfettered by ”a priori" legal categories which often derive from the exercise of legislative power in the same constitutional writ."

In (1959 SCR 379: AIR 1958 SC 560) quoting a passage from the Broken Hill South Ltd. v. Commissioner of Taxation, N.S.W. 56 CLR 337 at p. 379