Face blindness

Hume, Treatise Book I Part iii, section 2 (my emphasis):

We readily suppose an object may continue individually the same, though several times absent from and present to the senses; and ascribe to it an identity, notwithstanding the interruption of the perception, whenever we conclude, that if we had kept our eye or hand constantly upon it, it would have conveyed an invariable and uninterrupted perception. But this conclusion beyond the impressions of our senses can be founded only on the connexion of cause and effect; nor can we otherwise have any security, that the object is not changed upon us, however much the new object may resemble that which was formerly present to the senses.

Back-reference guarantees sameness of subject. Perception doesn’t. Think of the Bunuel film where two actresses (Carole Bouquet and Angela Molina) play the same character (Conchita). I was one of the many people who were fooled into thinking they were the same actress, because of the identity of character. Think also of the meaning of ‘persona’, namely ‘mask’. This idea comes more easily to me I suppose because I suffer from ‘face blindness’. I find it hard to tell when I am meeting the same (relatively unfamiliar) person or not, and rely on tells such as hairstyle, build, age and so on. I am often embarrassed when I meet the same person in the same day but the lighting is different or they have dressed differently and I do not recognise them. I often have to bluff my way out of it. The world of strangers is literally like a world of masks without identity. My wife and daughter guide me through film plots.

Now it might be that perceptual ‘reference’, i.e. reidentification, is some guaranteed and fail safe way of acquiring rapport with the subject, so you always know that the same person is before you. But I think not. I think other people just have better visual processing powers, meaning that a person’s face is a kind of uniquely applying description or ‘look’ that only one person can have. A sort of visual haecceitas, but which is descriptive, for all that. Think of identical twins. Their visual description is the same, so it’s a qualitative identity, not a numerical one.

Indiscernibility of Identicals

One of the assumptions in the substitution problem was the indiscernibility of identicals:

Fa and a=b implies Fb

Is this always true? A slightly different way of expressing the law is that if Fa, and if 'a' denotes exactly what 'b' denotes then Fb. But in this form the law is clearly not valid. Suppose there is a shortage of red paint, and that only Ferraris are red. Then it follows that if Ferraris are fast, then red cars are fast, and conversely. But it does not follow that if John thinks Ferraris are fast, then he thinks that red cars are fast – perhaps he is imagining a red reliant Robin that he once saw. I.e. F = ‘John thinks that every – is fast’ and a = ‘Ferrari’ and b = ‘red car’. Then Fa and the fact that ‘a’ denotes everything that ‘b’ denotes does not entail Fb.

You will object that indiscernibility of identicals applies only when a and b are proper names. Proper names are referring terms, not common terms like ‘Ferrari’ or ‘red car’. I reply: what is a referring term? If it is defined as something to which indiscernibility of identicals necessarily applies, then the ‘Shakespeare’ arguments in the previous posts suggest that indiscernibility of identicals does not apply to ordinary proper names at all.