What is the difference between an illustration and a metaphor? Put like that the question seems more soluble than if you were to ask; ‘what is the difference between an analogy and a metaphor’? That might be like the difference between a quadruped and a donkey. Or not. Could an analogy when pushed turn into a metaphor? Yes. Could an analogy used for the purposes of philosophical illustration when taken in the wrong sense end up as a metaphor which distorts its original intent? Yes.
Let’s take the metaphor ‘losing your temper’. Probably a lot of people would not be aware that this is a craft analogy from the time when all edge tools were periodically ground to renew their edges in preparation for honing. If excessive pressure was applied on the grindstone over a period of time without cooling through dipping in water the tool would turn blue at the edge and lose its temper. It would not afterwards be able to hold an edge. So don’t get overheated under pressure like the knife and lose your temper. ‘Temper’ I suggest here has lost its connection with its original analogical roots. Besides you won’t be able to ‘cope’. (f. couper/cut)
How dependent is philosophy on analogies? ‘Foundationally’ I would say and when ‘my spade turns’ (Wittgenstein) I know this is a sound ‘footing’.
But the greatest thing by far is be to a master of metaphor. It is the one thing that cannot be learnt from others, and it also a sign of genius, since a good metaphor implies an intuitive perception of the similarity in dissimilars.(From Aristotle’s Poetics 22:1459)