The difference of individuals and
universal properties has been recognized at least since the time of
Aristotle. Indeed, it is obvious that the universal genus of horse is
not an individual horse, although on some reading Plato had treated
the genus just as one individual among others. Despite the
familiarity of the distinction, it is quite hard to say what exactly
differentiates universals from individuals.
Now, Thümmig suggests the rather
curious definition that individuals are fully determinate in every
way, while universals are still further determinable. The idea behind
the strange definition is actually rather simple. Take some general
class of things, such as vertebrates. Now, if we know that an animal
is a vertebrate, we know something of it – at least that it has a
vertebra. Still, many other characteristics of the said animal are
completely undetermined by its being a vertebrate, for instance,
whether it flies or not. Universal vertebrate is thus determined
through this collection of properties shared by all vertebrates. This collection does still not determine any concrete individual,
because a particular vertebrate has still some characteristics not
included in the collection.
Similarly, all concrete individuals
must be completely determined in respect of all possible characteristics (presumably there's an infinity of such possible characteristics). In other words, we cannot have an
individual thing that would neither have a certain characteristic nor not
have it: the individual must be determinately one or the other. Furthermore, nothing but a completed determination of possible characteristics could individuate a particular thing. One might object that it could still be possible that an
individual is identifiable through some incomplete list of
characteristics – for instance, George Washington can be plucked
out from the rest of the humanity by him being the first president of
United States, even if we didn't knew what he was called. But the
objection forgets that in Wolffian philosophy we are allowed to look
at other possible worlds. Thus, there could be another possible world
where the first president of United States was a man called Thomas
Jefferson, and the given description would not distinguish the two
possible first presidents. Note that while an individual is
determinate in all aspects, we might not be able to determine all its aspects.
Some universals and no individuals are
then clearly indeterminate in some respect, but Thümmig's definition suggests also
that all completely determinate things are individuals, but never universals.
This is a far more uncertain proposition. Suppose for instance that
we would know a particular rock and all its characteristics
completely. Now, if we could then copy the rock and its exact
characteristics, we would have two different individuals with the
exactly same characteristics. In fact, the list of these
characteristics would be completely determined - this was the presupposition - but it would also
define a universal class containing several individuals (the two rocks).
Thümmig's definition thus clearly
presupposes the idea that no two individuals could have a matching
set of characteristics. This principle of the identity of indiscernibles originates actually from Leibniz, who according to a story once
challenged courtiers to look for two exactly similar leaves just to
prove the principle. Indeed, the principle might well be empirically
sound, but as the thought experiment shows, it shouldn't be really
accepted as an incontestable axiom of pure reason – and certainly
it should not be hidden within a definition. Still, Thümmig's
mistake is small when compared to what Baumgarten later did with the
same notions – more on this later.
Next time we shall look on animal
psychology.
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