Nothing is without a reason.
A monad is a simple substance without parts, extension or shape. Its whole life consists of perceptions, which represent many things in one, and appetitions, the tendencies that carry it from one perception to the next; monads have no windows through which anything could enter.
If a machine that thinks were enlarged to the size of a mill, a visitor inside would find only parts pushing one another and never a perception.
Since created substances do not act on one another, God arranged their states from the beginning so that each unfolds by its own law while agreeing exactly with all the others; the union of soul and body is the most striking case.
Two clocks made by a perfect craftsman keep the same time without any link between them, because each was built to run true.
Alongside the principle of contradiction, which governs necessary truths, Leibniz holds that nothing is or happens without a sufficient reason why it is so and not otherwise; applied to the whole series of contingent things, the principle leads to God as their last reason.
A balance with equal weights at equal distances stays level, since there is no reason for it to tip to one side rather than the other.
God’s understanding contains infinitely many possible worlds; his goodness chose, and his power created, the one that unites the greatest variety with the greatest order, even though it includes evils that a lesser world would have avoided.
A general prefers a great victory with a slight wound to a state without wound and without victory.