think of it as

How to spot it

The move is a comparison handed to you as an instruction: think of it as a thermostat, or imagine a world where the queue never forms. Both tell you to hold a familiar object in your head, and both arrive before the writer has said anything you could check about the subject underneath. Finding the phrase is the easy half, because it nearly always sits in the first line of a paragraph and announces itself. Deciding whether it earned its place takes one move. Cover the comparison with your hand and read the passage without it. If what is left still says what the subject is and how it behaves, the comparison was carrying a real idea into position, so put it back. If what is left says nothing, because every solid fact in the paragraph was riding inside the borrowed picture, the picture was standing where the explanation should have been.

Two further checks are worth running. An earned comparison is followed by work: the sentence after it spends the picture, mapping some part of it onto something particular about the subject. A reflex comparison is followed by generalities, and the subject never gets a plain sentence of its own anywhere on the page. The second check is cost. A writer who understands the material picks a comparison a reader could argue with, one that would be wrong if the subject turned out to work differently, while a comparison that would sit just as comfortably on any other topic has cost its author nothing.

Why models overdo it

Naming what a thing resembles can be done without any research behind it. The explanation it stands in for takes actual knowledge of the subject, and both cost a model the same to produce. A model choosing its next words is weighing what tends to follow, and after a topic sentence on almost any subject, an instruction to picture something is a likely continuation. It fits everywhere, which is another way of saying it belongs nowhere in particular.

The opening position makes this worse. That is where a draft has committed to the least and has the most left to fill, so that is where the borrowed picture tends to land, paragraph after paragraph, essay after essay. Nothing in that process asks what the comparison is being paid for. A writer pays by accepting that a reader can now test the picture against the thing itself, and gets a reader who arrives at the subject already holding something true about it. A model is not in that trade at all, which is why its comparisons read as decoration rather than as an argument.

When it's fine

The device is good, which is the part a suspicious reader forgets. Carl Sagan sent a general audience into a room awash in gasoline, with two enemies inside it counting matches, because the numbers he was actually arguing about had stopped meaning anything to anybody. Nine thousand warheads against seven thousand warheads is not an argument. It is two large numbers. Nine thousand matches and seven thousand matches in a room full of fumes is something a listener feels before the sentence has finished, and no briefing on yields and throw-weights was ever going to do that.

Christopher Hitchens used the same instruction to a different end. Closing a debate in 2010, he told the room not to treat an offer of certainty as a gift but to think of it as a poison chalice. Notice where that sits. The comparison lands after several minutes of argument, once he has said plainly what the offer is and what he believes it costs, so the picture is not doing the work of the case. It is the verdict on a case already made. That is probably the whole rule, and it costs nothing to apply. A comparison belongs in your draft when you can say what it is doing and the paragraph would still stand if a reader lifted it out. If lifting it out leaves nothing behind, replace it with the plain explanation.

Where it comes from

The shape is two older moves stacked on top of each other. Aristotle gave a chapter of the Rhetoric to the comparison half, separating a simile from a metaphor by one detail: the simile says the likeness out loud, as when Homer's Achilles rushed on like a lion, where the metaphor drops the like and calls him a lion outright. The scene a stock opener builds before it delivers that comparison has an old name of its own. Rhetoricians going back to Quintilian treated vivid description as a figure in its own right, hypotyposis, which handbooks still gloss as writing that leaves an audience feeling it watched a thing happen instead of hearing about it later. An order to imagine borrows the imperative mood to march a reader into that vividness. The vividness is what earns the name, not the instruction that asks for it.

Neither Aristotle nor Quintilian had a formula this fixed in mind, and what now reads as one stock hook is a marriage of the two performed long after both were dead. It survived for a practical reason. A listener cannot stop a speaker and ask for the diagram, so preachers built parables and orators built rooms, and both had an audience standing inside an idea before there was any way to argue with it. Advertising found the same trick useful from the other end, since a picture supplied early arrives before anybody thinks to ask for evidence, and a reader who has already imagined the room will usually accept the furniture that comes with it.