‘Where am I, or what? From what causes do I derive my existence, and to what condition shall I return?’ So asks the eighteenth-century philosopher David Hume as he sinks into ‘the most deplorable condition imaginable, inviron’d with the deepest darkness, and utterly depriv’d of the use of every member and faculty.’ What did Hume do when he felt like this? He tells us:

I dine, I play a game of back-gammon, I converse, and am merry with my friends

Now that’s an interesting response – I mean in terms of punctuation. ‘I dine’, ‘I play a game of backgammon’, ‘I converse’ – Hume presents us with a list of grammatically unconnected impressions. One might call it an ‘association of ideas’. (The reason one might call it that is because Hume was interested in the ways that one idea is associated with another.) What is the relationship between them? Well, that’s simple – it’s the repeated ‘I’. Given Hume’s despair is caused by the question ‘Where am I or what?’, this is a successful answer. ‘I’ appears as something these ideas have in common. But oh! Mr Hume, where have you gone at the end of your sentence? Yes, you dine, play backgammon, converse – but where is the ‘I’ that is ‘merry with my friends’? I see the list. I see the comma. I note the expectation of an ‘I’. But there is no ‘I’. You have dropped out of your own sentence, Mr Hume, just when I thought you’d found yourself in it! Still, at least you kept things together for a while. Perhaps that’s all we can ever hope for?

(David Hume gathers these impressions in A Treatise of Human Nature (1739–40), Book 1, Part 4, Section 7.)