What is Necessary Implication?

Legal Definition
In construing a will, necessary implication means not natural necessity, but so strong a probability of intention that an intention contrary to that which is imputed to the testator cannot be supposed. Wilkinson v. Adam, 1 Ves. & B. 466; Gilbert v. Craddock, 67 Kan. 346, 72 Pac. 869; Whitfield v. Garris, 134 N. C. 24, 45 S. E. 904.
-- Black's Law Dictionary