Locke grab bag 
I am teaching our undergraduate Descartes-to-Kant course this term. Rather than sprinting through seven thinkers, I just do five. And I don't even do that much Locke. Since we only have a week and a half on Locke - and since Locke's Essay is such a wide-ranging book - I target three topics: innate ideas, personal identity, and abstract ideas.

These three topics can seem unrelated. I tell students that they can think of them as a grab bag: the first as an answer to Descartes, the second as a fun diversion, and the third as an anticipation of Berkeley. They show the class the broad features of Locke's picture of the mind and language, but not in a systematic way.

1. Locke's arguments that there are no innate ideas provide a contrast with Descartes, who the class has just discussed. Without the concept of God as innate, the causal argument of Meditation 3 collapses. Berkeley, who we read next, thinks that Locke is so convincing on this point that there is no need to say anything further about the matter.

2. The concept of personal identity does not arise for Descartes or for Berkeley, but it is fun. The issue basically begins with Locke, and it's a antidote to the idea that philosophical topics are all timeless.

3. Berkeley spends the entire introduction to the Principles arguing that there are no abstract ideas. We get to that next week, and Locke's arguments for the existence of abstract ideas give some context.

Yesterday, the last day on Locke covered his distinction between nominal and real essences. I noticed two ways in which the topics integrate which I hadn't noticed when I taught this last time.

A one-two punch against rationalism

When one rationally reflects on what is essential in some idea, according to Locke, one only learns about its nominal essence. That is, one learns about something one constructed from experience. One learns nothing about existence beyond one's own mind.

So rationalism is hopeless, and the account of nominal essences wrecks Descartes' Meditation 5 argument for the existence of God. It is a nice one-two combo with the attack on innate ideas.

Real essences and identity

In addition to its nominal essence, an idea has a real essence which is whatever in the world is responsible for objects fulfilling the conditions of the nominal essence. Locke writes that we do not know anything about real essences, although he favors the corpuscularian conjecture that it is some unknown arrangement of parts.

The optimistic reading of Locke is that he thought real essences were unknown because he was writing long before molecular chemistry and atomic physics. Now we know (say the optimists) that the real essence of gold is for the stuff to have 79 protons in the nuclei of its atoms.

The pessimistic reading of Locke is that he thought, in principle, that we could never know the real essences of things. An advocate of this reading might say: The specification that gold is atomic number 79 counts as a change to the nominal essence; the idea of gold changed a bit with the development of atomic theory. Alternately, an advocate might refuse to play the game of guessing what Locke would say if he knew later science.

I am not up on the secondary literature enough to know which of these readings predominates. I personally suspect that the text can sustain either interpretation, given sufficient interpretive ingenuity. Yesterday, however, I noticed an interesting argument for the pessimistic reading.

Suppose we want to know the real essence of HORSE, for example. Different horses have separate material compositions, in the sense that they have distinct bodies. Moreover, they are not qualitatively identical. So every horse is a numerically distinct HORSE. To know the real essence, we nevertheless need to recognize BUCEPHALUS and TRIGGER as having the same constitution.

In the discussion of personal identity, Locke gives us a general account of what is involved in recognizing two things as the same. It always involves the principle of individuation for some governing idea. So there is no sense of asking whether BUCEPHALUS and TRIGGER have the same constitution simpliciter. Rather, we are asking whether they are of the same SPECIES.

Similarly: To identify two samples of GOLD as sharing a constitution, we implicitly apply the principle of individuation for ELEMENT.

This means, however, that a judgement about a real essence is in part determined by the sortal idea that we are employing. Such abstract ideas are always our own inventions and tell us nothing about the world. The upshot of this (considering Locke's views both on personal identity and on abstract ideas) is that claims about real essences are doomed never to successfully pick out mind independent structures of the world.


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