As the dualism of extension and thought is reduced from a substantial to an attributive distinction, so individual bodies and minds, motions and thoughts, are degraded a stage further.  Individual things lack independence of every sort.  The individual is, as a determinate finite thing, burdened with negation and limitation, for every determination includes a negation; that which is truly real in the individual is God.  Finite things are modi of the infinite substance, mere states, variable states, of God.  By themselves they are nothing, since out of God nothing exists.  They possess existence only in so far as they are conceived in their connection with the infinite, that is, as transitory forms of the unchangeable substance.  They are not in themselves, but in another, in God, and are conceived only in God.  They are mere affections of the divine attributes, and must be considered as such.

To the two attributes correspond two classes of modes.  The most important modifications of extension are rest and motion.  Among the modes of thought are understanding and will.  These belong in the sphere of determinate and transitory being and do not hold of the natura naturans:  God is exalted above all modality, above will and understanding, as above motion and rest.  We must not assert of the natura naturata (the world as the sum of all modes), as of the natura naturans, that its essence involves existence (I. prop. 24):  we can conceive finite things as non-existent, as well as existent (Epist. 29).  This constitutes their “contingency,” which must by no means be interpreted as lawlessness.  On the contrary, all that takes place in the world is most rigorously determined; every individual, finite, determinate thing and event is determined to its existence and action by another similarly finite and determinate thing or event, and this cause is, in turn, determined in its existence and action by a further finite mode, and so on to infinity (I. prop. 28).  Because of this endlessness in the series there is no first or ultimate cause in the phenomenal world; all finite causes are second causes; the primary cause lies within the sphere of the infinite and is God himself.  The modes are all subject to the constraint of an unbroken and endless nexus of efficient causes, which leaves room neither for chance, nor choice, nor ends.  Nothing can be or happen otherwise than as it is and happens (I. prop. 29, 33).

The causal chain appears in two forms:  a mode of extension has its producing ground in a second mode of extension; a mode of thought can be caused only by another mode of thought—­each individual thing is determined by one of its own kind.  The two series proceed side by side, without a member of either ever being able to interfere in the other or to effect anything in it—­a motion can never produce anything but other motions, an idea can result only in other ideas; the body can never