Nothing is in the intellect that was not first in the senses, except the intellect itself. - Gottfried Wilhelm Leibniz

Nothing is necessitated whose opposite is possible.

[...] Et celui de la raison suffisante, en vertu duquel nous considérons qu’aucun fait ne saurait se trouver vrai, ou existant, aucune énonciation véritable, sans qu’il y ait une raison suffisante pourquoi il en soit ainsi et non pas autrement. Quoique ces raisons le plus souvent ne puissent point nous être connues.
[sect. 32]

To the possible objection that thus the world would of necessity have long ago turned into a paradise, it is easy to reply: Many substances already may have attained great perfection; yet, the continuum being infinitely divisible, there will always remain in the unfathomable depth of the universe some somnolent elements which are still to be awakened, developed, and improved - in a word, promoted to higher culture. This is why the end of progress can never be attained.