"There must be simple substances, since there are composites; for the composite is nothing more than a collection, or aggregate, of simples."Son of a professor of philosophy at Leipzig University, Gottfried Leibniz started reading metaphysics at an early age. He studied mathematics at Jena and then law at Altdorf. Rejecting a professorship, he entered the service of the Archbishop of Mainz. Religion and the reunion of the Christian churches split by differences of dogma became a lifelong obsession. From 1673 on, he became courtier to succession of Electors of Hanover and librarian to the court library. A diplomatic mission to Paris in 1676 introduced him to many of the leading thinkers of the day and gave him the oportunity to visit Spinoza on the return journey.(Monadology )
It was during this time that he invented the infinitesimal calculus unaware of Newton's similar and prior achievement. The argument between the two over precedence and ownership was bitter. Leibniz' interest in abstract logical calculi was partly the result of his search for an ideal and universal language. In such a language, each simple idea was to be represented by a single symbol, and the rules for combination to be so simple and clear that it would be possible to decide mechanically which combinations were possible, which not. Disputed questions could be determined by calculation and a universal encyclopedia could contain a summary of all human knowledge.
Leibniz' logic distinguishes between truths of reason, which are necessarily true, and truths of fact, which can be logically contradicted. Truths of reason are, by nature, analytic: "When a truth is necessary, the reason for it can be found by analysis, that is, by resolving it into simpler ideas and truths until the primary ones are reached.". Such truths can be deduced by following a logical mathematical procedure. From a human viewpoint, truths of fact, are synthetic and finite. Their truth can only be be discovered through empirical means and they can be logically contradicted. From a theological viewpoint, however, truths of fact can be regarded as analytic and infinite - in the mind of God, that is. This latter conclusion derives from Leibniz' unique view of God and His relation to His creation.
Leibniz conceived of the world of created beings in terms of monads, primary immaterial simple substances with the properties only of mind. Where we conceive of bodies as composed of cellular units, Leibniz saw them as composed of immaterial and immortal units capable of internal drive or "appetition". Within the human, the dominant monad was the soul. "It follows that every soul is a world apart, independent of everything else except God; that it is not only immortal ... but that it keeps in its substance traces of all that happens to it." (Letter to Arnauld) Leibniz was commited to the "principle of sufficient reason" , that for every state of affairs, there is a sufficient reason for it being so and not otherwise. The "Theodicy" applies this principle to God and his creation and concludes that God must have sufficient reason for creating the world as it is . Given God's moral perfection, this must be the the best possible world and from the Divine viewpoint, all possible properties of an individual subject must be necessary.