I don't see why it matters at all whether we say that "all humans have the following similarities" as opposed to our saying "all uses of the term 'human" have the following similarities." — Hanover
Ah this is a common misconception. There are n + s conditions for both, and they are different. We need to analyse both conditions of description as well as ontology to get the proper picture.
Say, as I will now claim, the necessary and sufficient conditions for being a screwdriver (i.e. ontology) are ‘created to drive screws’. If so, the screwdriver
itself needs to fit entirely within the conditions ‘created to drive screws’. As a result screwdrivers must be created to drive screws only. A multifunction tool that is created to drive screws as well as say, cut rope, pick food from your teeth and file your nails would not fit in the conditions ‘created to drive screws’ and thus not fit the definition of ‘screwdriver’ even though such multifunction tools are created to drive screws! This counter-intuitive result is important so I will attempt to set it out below in a different iteration.
As mentioned there are different conditions between correctly describing things as x, as to whether something is x. Of course the two are related, we often describe things as x if they are x.
The necessary and sufficiently conditions of correctly describing x as:
1) “A screwdriver”
are if and only if:
1a) x is a screwdriver
however the conditions of being
1b) A screwdriver
as I claim, has one necessary and sufficient condition - if and only if:
1c) created to drive screws
That condition 1c) is obviously met if and only if x is created to drive screws. A multifunction tool then that is created to do things over and above drive screws (like our aforementioned example that is also created to pick from food from your teeth) and would thus not be a screwdriver.
But confusingly there are also conditions that need to be met in order to be
described as:
2) “created to drive screws”
Note that 2) is different from the conditions that are 1c) created to drive screws. 2) and 1c) differ in that 2) is a description while 1c) are a set of conditions (for ontology).
To be 2) described as “created to drive screws” there is only one necessary and sufficient condition, if and only if:
2a) x is created to drive screws.
Notice however that 1c) uses the description 2)!
Multifunction tools, and screwdrivers, then that both meet 2a) and can be described as being 2) created to drive screws. Things that meet 2a) however do not necessarily meet 1c). Indeed our multifunction tools that meets 2a) by being created to drive screws because they are not created to drive screws exclusively, do not meet 1c (and therefore not 1b), 1a) or 1)) and cannot then be screwdrivers, nor can correctly be described as such.
Note there is no infinite regression here. 2a) uses 2) and 2) uses 2a), not a further description which would be a problem if that description needed a description that needed a description and so on.
Using this method of understanding necessary and sufficient conditions, let us re-examine one of the few uncontroversial essentialist definitions - the example of ‘bachelor’- and examine why it is so uncontroversial.
The conditions of being correctly described as
3) “a bachelor”
(as opposed to being a bachelor) are if and only if:
3a) x is a bachelor
the conditions of being a bachelor however are if and only if x is:
3b) an unmarried man
uncontroversially, the conditions of being correctly described as ‘unmarried’ are:
3c) unmarried
and the conditions of being correctly described as a man are:
3d) a man
The reason that the conditions for ontology (3b) are uncontroversial is because unlike ‘screwdriver’ not only is every unmarried man necessarily 3c) unmarried and 3d) a man, but that all things 3c) unmarried and 3d) a man can be correctly described as ‘unmarried’ and ‘a man’. This follows, as people are described as ‘unmarried’, for example, only need to be unmarried. Although this would theoretically include anyone over and above ‘married’, married people can’t be over and above married (as opposed to over and above ‘created to drive screws’). This is due to marriage being a binary - it being absurd to be married and unmarried, say, unlike the way that multifunction tools that can be created to drive screws and created to pick food from teeth. This binary effect, also present in the quantifier ‘a’, the sex ‘male’, and species ‘human’ result in it being, in some sense, an accident of circumstance that the conditions of ‘bachelor’ works both as a description and also ontology.
The distinction between description and ontology is vital to defining things but can be hard to accept at an intuitive level. Under the distinction that I’ve made here, a vegan diet can be defined as having necessary and sufficient conditions (i.e. of ontology) of:
4a) eating non-animal products
It would be a mistake though, to suggest that an omnivore - say chewing on a cheeseburger with a piece of lettuce in - is following a vegan diet just because she is
eating non-animal products. Why is this? Intuitively it seems as though our cheeseburger fan is eating non-animal products and should therefore meets the diet of 4a). The answer though, is that a sentence that includes ‘eating non-animal products’ (as per the italicised portion of the first sentence in this paragraph) itself is a description, rather than what I am calling conditions of ontology. It is the fact that a vegan diet is exclusively eating non-animal product that makes it vegan, and it is exclusively the diet that is exclusively eating non-animal product that can correctly be described as vegan. We should be able to see here that the idea that ‘eating non-animal products’ has its own necessary and sufficient conditions is just another way of phrasing the fact of distinction between description and ontology. To ignore this distinction however would be a serious mistake when defining concepts and thinking about essentialism.