A new type of the deductive principle (named the saturation one) is introduced for a linear temporal logic with o(”next”) and W(”unless”). The saturation replaces induction-like postulates and intuitively corresponds to a certain type of regularity in the derivations for the logic. Non-logical axioms in ”saturated calculi” are some sequents, indicating the saturation of the derivation process in these calculi. The finitary saturation suggests that ”nothing essentially new” can be obtained continuing the derivation process. An infinitary saturated calculus instead of an ω-type rule of inference has an infinite set of ”saturated” sequents, but the form of these sequents is uniform. The saturation presents a unique deductive principle both for finitary and infinitary cases. The derivability in a finitary saturated calculus (decidability of a saturated calculus) serves as a finitary completeness (decidability, respectively) criterion for the first order linear temporal logic.