Regarding II: how is the essence of truth understood in the pre-Kantian metaphysics of the eighteenth century, which is supposed to present the highest human realization in the field of metaphysical cognition?
According to the traditional concept, truth (veritas) is the adaequatio intellectus et rei, the correspondence of thought and thing; instead of adaequatio one also says commensuratio or convenientia, conformity or agreement. This essential determination of truth is ambivalent, the ambivalence of which also guided the question of truth already in the Middle Ages. There still lies over it the reflection and afterglow [Ab- und Nachglanz] of a formerly more original, if also scarcely comprehended, experience of the essence of truth in the inception of Greek Dasein. As adaequatio, truth is a determination of ratio, the assertion, the proposition. A proposition is true insofar as it corresponds to things. But the definition of truth as correspondence holds not only for the proposition in relation to things but also for the proposition in relation of things [themselves], insofar as they relate, as created, to the plan of a creative spirit and are in accordance with this. Seen in this way, truth is the conformity of things with their essence as conceived by God.
We are asking in a comparable way: how does the essential definition of truth run in modern metaphysics? In §92 of his Metaphysica, Baumgarten offers the following definition: veritas metaphysica potest definiri per convenientiam entis cum principiis catholicis. “Metaphysical truth,” i.e., the truth of metaphysical cognition, “can be defined as agreement of beings with the most universal principles of all.” Principia catholica are precisely the principles (axioms) that are “catholic” (in accordance with the Greek καθόλου), i.e., the principles directed toward the whole that assert something of beings as a whole and of the being of beings as such. All metaphysical propositions that establish being and its determinateness must accord with these principles. These principles [119] are the iron-clad propositions of reason itself: the principle of the I, the principle of contradiction, and the principle of sufficient reason. The truth about what things in their thingness are is determined on the basis of principles of pure reason, i.e., in the essential sense characterized earlier, namely mathematical. The inner structure of metaphysics as a whole must be formed in accordance with this concept of truth. We come to the third question.
Regarding III: what is the inner structure of this metaphysics? We can already gather a few things from the external division and sequence of the disciplines. The foundation is ontology, and the apex of the structure is theology. The former deals with what belongs to a thing as such, to a being in general (or in communi), to the ens commune; the latter, theology, concerns the highest and most authentic being absolutely, the summum ens. In terms of content, we also find this arrangement in the metaphysics of the Middle Ages, even already in Aristotle. But what is decisive is that, along the way,