The world we experience is clearly a world of interacting things, and one rarely finds anything that is completely isolated from its environment. Despite this evident importance, relations have often been relegated into a subservient position in traditional ontologies. It is like philosophers were interested only of classifying things into neat categories, but when it comes to explaining their interconnections, they soon loose their interest. It is then no wonder that Wolffian theory of relations is presented almost as an afterthought, attached to the discussion of complex and simple substances.
Wolff begins with the general notion that a thing is related to another thing – this happens when we consider two things together in such a manner that one of them cannot be understood without a reference to another. Thus, when we think of a person as a parent, we must think of some other person who is a child of this parent. Now, many things could be considered without such a reference to something else, just like we can describe George Bush Senior, without ever invoking any reference to other human beings. Still, we might also consider some aspect of Bush Senior that requires an essential reference to another person, for instance, when we see him as a father of Bush Junior.
These aspects then are relations. Note that with Wolff's definition it is natural to single out the subject of relation, thinking of which requires the reference to someone else, just like consideration of a father requires at least implicit reference to someone to whom he is the father. It just now dawns to Wolff that he has already described several relations, such as equality of quantities or similarity of qualities. There is still no indication that he would have felt a need to transfer his general account of relations to an earlier position in the book.
An important relation is the one between that which contains a reason (principle) for something else (principate). Thus, as forces are a reason for changes in substances, they could be called the principle of change. This leads to a new possible definition of substance. Changes of finite simple substances are based on their inner force and changes of composite substances are ultimately based on the inner forces of their constituent substances, thus all finite substances contain in themselves a principle of change. Then again, accidences cannot really change – that is part of their definition – thus, they also cannot have any principle of change. This only leaves infinite substance out of account, as Wolff admits it cannot really change. Still, Wolff can always fall back to the option of saying that an infinite substance has eminently a principle of change in itself (it does some have force, evidently). Thus, substances can be defined as those entities that have a principle of change in themselves.
Wolff also defines species of different principles. Some principles contain reason for possibilities – in this sense essences are principles of things being modified in a certain manner – while others contain reason for something actually occurring – in this sense modes and other things are principles of thing being modified in a certain manner. Beyond these, there are also cognitive principles, which are essentially propositions explaining other propositions.
Probably the most important point in defining the notion of principle lies in explicating the concept of cause. Simply put, cause for Wolff means a principle, on which the existence of something different depends. Wolff's definition of cause extends far beyond what nowadays is usually called cause, because even if Wolffian cause differs from what it causes, it might still be an aspect or part of the caused, as long as it contributes to understanding why this thing exists. Thus, it is no wonder that Wolff mentions Aristotelian notions of formal and material cause, the former being identified with the essence of the caused, the latter with the constituent parts of the caused, if it has any.
The important notion of cause from the modern point of view is then efficient cause, which Wolff defines as a cause, the causality of which consists of actions – that is, which acts and thus explains the existence of something else. As Wolff's notion of activity is essentially connected with the concept of force, his idea of efficient causality is based on the traditional mechanistic scheme of bodies striking one another and transmitting movement (needless to say, there is no indication in Wolff of the Humean problem how we can recognise causal interactions). Wolff also notes that often one efficient cause is not enough, but the existence of something has required action of many causes, and that efficient causes form series, in which more distant causes lead on to more proximate causes.
Finally, final causes Wolff defines as reasons why an efficient cause starts to act. Final causes are thus causes for efficient causes and thus must precede them, which is only possible, Wolff concludes, if there has been some entity which has previously thought these ends and now decides to actualise them. In effect, Wolff denies the existence of ends without any conscious beings that can set ends to things. Thus, although he has borrowed his scheme of four causes from Aristotle, he clearly rejects some essential underpinnings of the scheme – all events might not have intrinsic final cause. Then again, since Wolff also supposes the existence of an infinite entity or God that has created the world because of its perfection, he would have to admit that all things have some extrinsic end.
In addition to cause, the only relation Wolff dedicates a whole chapter on is the relation between sign and signified. We may leave this topic almost completely untouched and just mention that Wolff admits the possibility of natural signs, that is, things which by nature refer to other things.
So much for ontology then. Next time I will start by looking at a new generation of Wolffians.