Certainty and Necessity

As has been previously discussed, two seemingly minor terms in the often overlooked full title of Descartes' work on Method suggest not so minor flaws in the Method.  A third, more substantive, term implies a further shortcoming that is best illuminated by a development of one of his successors.  The term is Truth, which, as connoting Objectivity, contrasts sharply with the Subjectivity of the two main features of the Method--Certainty and Doubt, i. e. each of which is a subjective psychological condition. Descartes' ambition becomes clearer in the light of Leibniz' development of Modal Logic, i. e. what he is seeking in Certainty is actually an Objective condition--Necessity.  Likewise, subjective Doubt correlates to objective Contingency, demonstrable by a possible counter-example, e. g. a perception caused by a dream, rather than by a real object.  Now, the significance of Leibniz' innovation emerges historically long before the current pervasive reliance on Modal Logic--Necessity is the pivotal topic in the Hume-Kant debate over Causality, ingredient in which is an exercise of Skepticism that is different than Descartes', i. e. one that targets the connection of Sense-Data, rather than Sense-Data itself.  While the explicit target of this Empiricist Skepticism is the application of Modality to Sense-Experience, it originates in Locke's challenge to Descartes' premise that Doubting that one Doubts consists in two simultaneous propositions, and, hence, is subject to the Principle of Contradiction.  Instead, according to Locke's alternative analysis, Doubting that one Doubts is diachronic, constituted by two, successive, acts of Doubting, conjoined by memory.  Thus, even Descartes' Certainty is unestablished.  In contrast, Kant re-establishes Necessity by locating it beyond the ken of both Rationalist and Empiricist Skepticisms--in the Technical Reason of Schematism--and, hence, beyond the scope of Descartes' Method.