Metaphor uses comparison, association or resemblance to make an analogy between one thing and another (war and argument, or time and money). By contrast, metonymy uses an attribute of something to stand for the thing itself, or point to the thing itself by reference to its effects (smoke and fire, or brass and military officers). Synecdoche is a specific type of metonymy where a word for part of something is used to mean the whole (sail for boat, wheels for car, face for person). Irony (not so commonly written about in semiotics) is where words are used to convey a meaning contrary to the literal sense of the words, such as, ‘I love being tortured’ spoken by someone in pain (with a few weird exceptions). [Irony is one of the many reasons for the difficulty of semantic analysis by computers which are, so far, not sophisticated enough to interpret context.]