Analogy & Simile
analogy draws an explicit similarity relationship between things; a 16th century term, its closest Classical figure is simile, from the Latin similitudo, meaning 'like'

Examples

Literary Similes

Robert Burns
My love is like a red, red rose

P.G. Wodehouse
As sore as a sunburned neck

G.B. Shaw
A parson is like a doctor, my boy: he must face infection as a soldier must face bullets.

Victor Hugo
There was a quivering in the grass which seemed like the departure of souls.
Commonplace Similes

sleep like a log
drink like a fish
as bold as brass
as good as gold
as old as the hills
as drunk as a lord
as wise as an owl
as mad as a hatter
works like a charm
as cunning as a fox
as white as a sheet
as quiet as a mouse
as different as night and day

Purpose

Roland Barthes
Humanity seems doomed to analogy.
Analogy Describes & Categorizes
We commonly describe or categorize things in terms of other things. Analogy helps us describe and categorize a thing so that others can 'see' the thing described. Analogy aids cognition and shares similarities with descriptive figures like metaphor, metonymy, parody and simile. These 'analogies' describe complex things more vividly and familiarly.
Charles Dickens
[Dora's cousin was a man] with such long legs that he looked like the afternoon shadow of somebody else.
Analogy Explains
Analogies provide shortcuts for talking about complex things that are easier for non-experts to understand.
Theoretical physicist Gian Giudice explains the Higgs boson with analogies to water and air at TEDxCERN, 2013
Astrophysicist Neil deGrasse Tyson explains the success of space technologies with shaving and lawn-mowing analogies at the 28th National Space Symposium, 2012
Analogy Argues
Analogies can provide argumentative proofs. Reasoning by analogy establishes a logos proof through similarity, but not everyone accepts analogical reasoning like the examples below as valid arguments. Rhetoricians are more likely to accept arguments by analogy than logicians are.
Bill Maher compares Donald Trump's possible cabinet appointees to toddlers.
Analogy, Simile & Metaphor
Simile resembles extended metaphor. Technically, simile suggests relationship similarity but metaphor asserts actual similarity. Compare:
Analogy by Simile
The minister upholds the state like a pillar which supports the weight of the whole edifice.
General Ludendorff: The English soldiers fight like lions.
Analogy by Metaphor
The minister is a pillar of state.

General Hoffmann: But don't we know that they are lions led by donkeys?
Similes signal similarity with 'like' or 'as.' But other structures signal similes, and some similes are only implied. Similes without 'as' or 'like' are more likely considered analogies.
Simile by Comparison
The errors are more obvious than the sun.
The sound was harsher than fingernails scratching a blackboard.
His behaviour reminded me of the worst kind of insurance salesman.

P.G. Wodehouse
So might a fastidious cook look at a black beetle in her kitchen.
I got a headache that started at the soles of my feet and got worse all the way up.
Simile by Implication
Winston Churchill
As his [Hitler's] armies advance, whole districts are being exterminated. Scores of thousands, literally scores of thousands of executions in cold blood are being perpetrated by the German police troops upon the Russian patriots who defend their native soil. Since the Mongol invasions of Europe in the sixteenth century there has never been methodical, merciless butchery on such a scale or approaching such a scale. And this is but the beginning. Famine and pestilence have yet to follow in the bloody ruts of Hitler's tanks. We are in the presence of a crime without a name.

Usage

Analogies are commonplace and persuasive. We can use them to:
provide proofs:
​describe vividly:
simplify complexity:
categorize efficiently:
Is the thing good/bad or right/wrong?
What is the thing like?
What is the thing like?
What is the thing?
Make Analogies Fresh, Vivid & Precise
P.G. Wodehouse
He started to get pink in the ears and then in the nose and then in the cheeks till in about a quarter of a minute he looked pretty much like an explosion in a tomato cannery on a sunset evening.
Make your analogies fresh, vivid and precise. Imprecise analogies are as ineffective as mixed or faulty metaphors. Avoid also clichéd analogies. Arguments by analogy must be precise or audiences will invalidate them.
Compare these vivid and humorous similes from P.G. Wodehouse with less successful ones compiled by the Washington Post:
Good Similes of P.G. Wodehouse
  • A brain like a buzz saw
  • As imperious as a traffic cop
  • He writhed like an electric fan.
  • He beamed like the rising sun.
  • As sober as a teetotal girl guide
  • He vanished like an eel into mud.
  • I came out like a pickled onion on a fork.
  • He looked like a sheep with a secret sorrow.
  • She looked like Helen of Troy after a good facial.
  • It stimulated him like a cactus in the trouser seat.
  • A hissing noise, like a tyre bursting in a nest of cobras.​
  • A laugh like a squadron of cavalry charging over a tin bridge
  • She looked like a horse that is worried about the quality of its oats.
  • The sort of look a thoughtful vulture in the Sahara casts at a dying camel
  • I tottered, swayed and came down like some noble tree beneath the woodman's axe.
  • [The butler] had that strained air of being on the very point of bursting which one sees in frogs and toy balloons.
  • Mac had many admirable qualities, but not tact. He was the sort of man who would have tried to cheer Napoleon up by talking about the winter sports at Moscow.
  • He was in much the same position as a general who, with his strategic plans all polished and ready to be carried out, finds that his army has gone off somewhere, leaving no address.
  • Like most men who saw her for the first time, he experienced the sensation of one in an express lift at the tenth floor going down who has left the majority of his internal organs up on the twenty-second.
Bad Similes of School Students
  • He was as tall as a 6'3" tree.
  • Her vocabulary was as bad as, like, whatever.
  • The A-Frame Structure stood like an inverted V.
  • The lamp just sat there, like an inanimate object.
  • He was the size and shape of a man much larger than him.
  • The red brick wall was the color of a brick-red Crayola crayon.
  • Her eyes were like two brown circles with big black dots in the centre.
  • The situation had become topsy-turvy — like Christmas in the summer, if you're in Australia.
  • The little boat gently drifted across the pond exactly the way a bowling ball wouldn't.
  • The young fighter had a hungry look, the kind you get from not eating for a while.
  • Then he kissed her, like a butterfly kisses the windshield of a Porsche on the Autobahn.
  • The ballerina rose gracefully en pointe and extended one slender leg behind her, like a dog at a fire hydrant.
  • Editing is just like writing, except hateful, and in reverse. Instead of birthing words and ideas out of nothing, you're murdering them in cold blood, culling them like sickly sheep, weakening the flock.