There’s a lot online already about figurative language, some of it of more use than others. However, I thought It might be useful to go over, in brief terms, the difference between: Irony, Metaphor, Metonymy, and Synecdoche. Wikipedia has pretty good entries on each of these as well, so feel free to go there if you like.
Irony is perhaps the best known but also most misunderstood of the figurative tropes. Broadly, and we’ll go from the Wikipedia entry for this one, irony is
‘a literary or rhetorical device, in which there is an incongruity or discordance between what one says or does and what one means or what is generally understood.”
Or, according to Harold Bloom in his ‘The Art of Reading poetry’:
‘…saying one thing while meaning something so different that it can be the precise opposite. We learn to wince when Hamlet says: “I humbly thank you” or its equivalent, since the prince generally is neither humble nor grateful.’
Metaphor, also, is well known and well understood. In simple terms it is the transfer of characteristics of one object to another. So if you say ‘The office-building was a tomb’ you take those meanings commonly associated with tombs, those of death, stillness, morbidity and so on, and overlay them onto the understanding of an office. Wikipedia offers a good example, it says:
The metaphor, according to I. A. Richards in The Philosophy of Rhetoric (1936), consists of two parts: the tenor and vehicle. The tenor is the subject to which attributes are ascribed. The vehicle is the subject from which the attributes are borrowed. Other writers employ the general terms ground and figure to denote what Richards identifies as the tenor and vehicle. Consider the All the world’s a stage monologue from As You Like It:
And all the men and women merely players;
They have their exits and their entrances;
— (William Shakespeare, As You Like It, 2/7)
All the world’s a stage,
In this example, “the world” is compared to a stage, the aim being to describe the world by taking well-known attributes from the stage. In this case, “the world” is the tenor and “a stage” is the vehicle. “Men and women” are a secondary tenor and “players” is the vehicle for this secondary tenor.
Synecdoche is different to both Irony and Metaphor, but it is just as concrete in its implications. It represents a trope where a ‘part’ is substituted for a ‘whole’. The common example of this is ’50 head of cattle’ where the heads are counted in order to represent the whole animal. The whole is implied by the presence of the part.
Metonymy, finally, is where something is referred to in terms of something it is closely associated with. This is different from synecdoche, where the two elements being summoned must be part of the same whole. Instead, in metonymy, the requirement for referral is one of ‘intimate association’. As Harold Bloom says: ‘The name or prime aspect of something is sufficient to indicate it.’ So, for example, in the line ‘Lend me your ears’, ‘ears’ is used to refer to hearing, or attention, as there is a common understanding of association between the two.
It is tempting to boil these few tropes down to a calculus of language, (e.g. irony = using A to say B. Metaphor = taking elements of A and assigning them to B) however, as in much of language, the practical divides between irony, metaphor, synecdoche and metonymy are thin and fungible. I suggest further reading. Leave a comment below if you have any ideas of the next place to look.