Plato on loving things for the sake of other things

“‘All right then,’ I said. ‘Now that we’ve got as far as this, boys, let’s be careful not to be deceived.’ …

‘Let’s consider the following case: medicine, we say, is a friend for the sake of health.’

‘Yes.’

‘Is health a friend too, then?’

‘Of course.’

‘If it is a friend, it is so for the sake of something.’

‘Yes.’

‘And that something is a friend, if it is to be consistent with what we admitted earlier.’

‘Of course.’

‘And that too, in its turn, will be a friend for the sake of a friend?’

‘Yes.’

‘Well then, ...