Gottfried Leibniz

It follows from what we have just said, that the natural changes of monads come from an internal principle, since an external cause would be unable to influence their inner being. ”

I maintain also that substances, whether material or immaterial, cannot be conceived in their bare essence without any activity, activity being of the essence of substance in general. ”

I do not conceive of any reality at all as without genuine unity. ”

Men act like brutes in so far as the sequences of their perceptions arise through the principle of memory only, like those empirical physicians who have mere practice without theory. ”

But in simple substances the influence of one monad over another is ideal only. ”

Whence it follows that God is absolutely perfect, since perfection is nothing but magnitude of positive reality, in the strict sense, setting aside the limits or bounds in things which are limited. ”

Music is the pleasure the human mind experiences from counting without being aware that it is counting. ”

I hold that the mark of a genuine idea is that its possibility can be proved, either a priori by conceiving its cause or reason, or a posteriori when experience teaches us that it is in fact in nature. ”

For since it is impossible for a created monad to have a physical influence on the inner nature of another, this is the only way in which one can be dependent on another. ”

Indeed every monad must be different from every other. For there are never in nature two beings, which are precisely alike, and in which it is not possible to find some difference which is internal, or based on some intrinsic quality. ”