In the Discourse on Metaphysics Leibniz gives an account of substance which is more than peculiar.  Substances, being a temporal expression of the infinite, contain a complete concept of themselves wholly independent from all other substances.  This complete concept of substance involves his notion of truth, as well as his take on the nature of substance.  Leibniz states in the New System of Nature that “God originally created the soul (or any other perfect unity) in such a way that everything must arise for it from its own depths … having a perfect spontaneity relative to itself” (AG, pg143).  The idea that a substance might contain all of its causes within itself is at the same time supportive of the idea of human freedom as well as destructive.  The basis for human freedom in Leibniz’s system of the Metaphysics is entirely dependent upon the possibility of other creations and this still is problematic for him.

The definition of necessity and truth given by Leibniz is that a thing is only necessary if its negation does not imply a contradiction. The statement “a star is a ball of burning gas” is true because the idea of “a ball of burning gas” is implied by the word ‘star’, and to state the opposite, that “a star is not a ball of burning gas” implies a contradiction and is therefore false.  The same is true for substances.  Every predicate that may be said of a given substance is contained within the very notion of the substance.  This means that given the idea of any substance, every predicate which is true of this substance is already contained within it.  The idea that all true predicates of a substance are already contained within its complete concept is problematic because this includes any predicates which have yet to occur in temporal reality.  The statement “I will eat dinner at 5:30 tonight” is either already contained within my complete concept or it isn’t based upon the contingency of God’s will.  This may appear to be a problem for some because it implies that these statements are already true despite what we would choose and it impedes upon the idea of human free will.  The truth of these statements contained within the complete concept of a substance is not knowable to anyone aside from God, and he knows even a priori the condition of these statements (AG, pg41).  Leibniz attempts to show that despite the truth of these statements already having been determined, we are still free agents in that there is the possibility of other existences wherein these statements differ (AG, Part 13).  He also goes so far as to say that were these truths altered in the slightest we would cease to be who we are, because it is these very predicates which make up the identity of a substance.  Also, it would necessitate the altering of this very existence were any of these statements altered because of the idea that each substance is a temporal expression of all things in existence (AG, pg41-42).  The complete concept of each individual substance, then, contains all statements which may be said of it. Whether they pertain to what we might perceive as past, present or future is irrelevant because the substance is by nature infinite.

            Leibniz differentiates between hypothetical and absolute necessity when writing to Arnould as well as in part 13 of the Discourse on Metaphysics.  He explains that there is an absolute necessity in mathematical or geometrical truths, such as the necessity that all points of a circle are equidistant from its center, because its negation would result in a contradiction, but in hypothetical necessity the statement may be negated without issue.  “..Nothing is necessary whose contrary is possible” (AG, pg46).  The negation of the statement “I will eat dinner at 5:30 tonight” does not necessarily result in a contradiction; it is contingent upon whether or not this statement is true for my complete concept.  The existence of other possible worlds or existences makes it apparent that the necessity of all things is contingent upon which world God has chosen to create.  All things in this world then are contingent so long as God had the ability to choose another world to make instead of this one.  The logical question to ask here then is, did God actually choose this world or was he forced by his nature to create it?  If God necessarily created this world as opposed to another, then there is no contingency and therefore no freedom. 

Leibniz discusses the nature of God in the first parts of the discourse. He attributes God to be “an absolutely perfect being” and that though “there are several entirely different perfections in nature … God possesses all of them … in the highest degree” (AG, pg 35).  Leibniz claims that through God’s perfections, he must have created a world which is the best of all possible worlds.  This best of all possible worlds according to Leibniz must have been created as opposed to another because of the attributes of God.  It is unclear then, if God must have created the best of all possible worlds by his own nature, how he would then have the ability to choose one existence over another.  If God’s own attributes necessitate him to will into existence one world rather than another, there is no contingency at play.

An important feature of substance in Leibniz’s Discourse is that each substance is an expression of the universe and contains within it an expression or reflection of all other substances within it.  This is not to say that every substance is contained with all others, or that they reflect God or the universe perfectly, “each one expresses in its own way, somewhat as the same city is variously represented depending upon the different positions from which it is viewed” (AG, pg42).  Because each substance contains within itself a complete concept which has all the true predicates about that substance as well as all causal relationships to which it belongs, it then must contain within its complete concept an image of all other substances.   This then seems to indicate that it is necessary that there be more than one substance outside of just God and one other substance.  Each substance, in a sense, necessitates the existence of all other substances.  The notion that a finite substance might necessitate the existence of another seems to be in opposition to the idea that finite substances are not causally related.  If a substance necessitates the existence of another then it must in some way cause that other to exist.  This problem might be defeated by Leibniz in the idea that when God creates the universe he creates all substances simultaneously as they can only exist by ‘creation’.  Substances are not made up of divisible components, or rather, that which makes up a substance is not divisible.  Therefore, for any substance to exist its constituent parts were created with the universe and all substances although seemingly necessitating the existence of each other, it is only a consequence of their existence in this universe which God has placed them in.  It relates to the idea of contingency and identity, if the substance were changed in any way, it would necessitate that all other substances in the universe were altered accordingly.  The existence of this universe requires that substance to be what it is and as it is impossible that there are two substances which only differ in number (AG, pg41-42) the existence of that substance is contingent upon the decisions which God had made at the time of creation.

            The concepts of necessity and contingency as presented by Leibniz rely entirely on the point that God freely chose to create the world.  The fact that Leibniz states that God through his perfect nature must choose to create the best possible world defeats his argument that God chose to do so freely.  There is then no chance that there is freedom or even contingency in any existence because the negation of any given statement would then negate the fact that God must have acted as He did.  If God is caused by necessity then all things which follow must also be necessary, what was once a contingent truth has become a necessary truth by virtue that God is the transcendent cause of all things.  The necessity of the existence of this universe is apparent through Leibniz’s own arguments.  Because God must have created this universe as opposed to something different, through his perfection and his reason, he must have chosen this one by necessity, therefore destroying the contingent existence of this world.  The only possibility to save the contingency of all things is to argue that God could have chosen not to create anything.  Because God did not create by necessity, the idea of the contingency of substance is preserved.  It is not that God chose to create this world that our existence is contingent, it is in the fact that God has chosen to create.