Ludwig Wittgenstein: the duty of genius | 
Imagine someone pointing to a spot on the iris in a face by Rembrandt and saying 'the wall in my room should be painted this colour.'
Imagine someone pointing to a spot on the iris in a face by Rembrandt and saying 'the wall in my room should be painted this colour.'
In one respect, at least, the ethos of the hard-boiled detective coincides with Wittgenstein's own: they both, in their different ways, decry the importance of their "science of logic", exemplified in the one case by Principia Mathematica and in the other by Sherlock Holmes.
The idea is that, if the contrary of a proposition makes sense, then that proposition can be regarded as an empirical hypothesis, its truth or falsehood being dependent on the way things stand in the world.
The moon was up. "If I had planned it", said Wittgenstein, "I should never have made the sun at all"
Freud's idea: in madness the lock is not destroyed, only altered; the old key can no longer unlock it, but it could be opened by a differently constructed key.
In teaching you philosophy I am like a guide showing you how to find your way around London. I have to take you through the city from north to south, from east to west, from Euston to the embankment and from Picadilly to the Marble Arch.