Here come the old metaphors again – and some new ones, too. In the last few days we have heard Barack Obama flooding the zone so as to urge strikes in Syria, within time windows, but without boots on the ground, because of the crossing of a red line which, back in May, threatened to box in the president, or even turn into a green light for Bashar al-Assad, who himself says that "the Middle East is a powder keg, and today the fuse is getting shorter". John Kerry calls people who hesitate "armchair isolationists", which suggests useless snoozers by the fireside rather than thoughtful opponents. Meanwhile, the media dubs France "America's poodle". So vivid are British memories of that taunt that the very thought of it may have accelerated the quick decision this time to reject military involvement.

Metaphors are powerful. They can herd us to war or hold us back from the brink (these being metaphors too). Yet meanings shift. Whole theses could be written on the history of armchairs and poodles. Indeed, in a discussion of the poodle trope at the University of Pennsylvania's Language Log site, contributors trace the present meaning of eager, obedient lackey back to at least 1907, when Lloyd George called the House of Lords the Earl of Balfour's poodle. Beyond that, poodles appeared differently in Goethe's Faust, where the devil Mephistopheles disguises himself as one. When his true shape is revealed, Faust cries, "Das also war des Pudels Kern!" – "So that was the poodle's core!" – which became a German catchphrase. It seems a world away from what the original breeders must have had in mind when they bred the Pudelhund to be an agile, intelligent water retriever. (And they actually make good war dogs.)

Once you start noticing the metaphors in everything you say, you realise how central they are to human ways of grasping the world. They are not merely an accident of language, but rooted in our minds and even bodies. This was the message of George Lakoff and Mark Johnson's 1980 book, Metaphors We Live By, which analysed such pre-linguistic "conceptual metaphors" as the idea that anger makes one boil over or explode, or that whatever is "up" is good and whatever is "down" is bad. This is why Kerry's armchair works: if you sit down, you are not stepping up to the plate.

This is also the reason why talk of military "strikes" is significant. The term is more metaphorical than it may sound, and calls to mind carefully aimed knock-out punches or lightning bolts. We are more likely to think of a sharp, effective blow than with "bomb", which brings to mind explosions, injuries, mess. Bombs imply a down and outward movement, with things pounded to bits. Strikes imply an into and through movement, which sounds nicer. Our response is physical and instinctive, just as with the up/down distinction.

All this would be of merely curious interest were it not for the fact that metaphors make a difference to how we do things. Research suggests that talk of economic bangs and collapses has self-fulfilling effects, and that people approach law enforcement differently according to whether they think of crime as a "spreading virus" or a "ravening beast". In medicine, metaphors of attack and defence can influence approaches to dealing with disease.

In politics, however, the situation is complicated by politicians' habit of using language to manipulate the public and each other. It is not easy to distinguish between a soundbite coined to placate the masses and a genuine conceptual metaphor to which the politicians themselves are in thrall, and of which they should beware.

Either way, once we start seeing something as a crossed line, a window of opportunity or a lightning strike, it can be hard to control our responses. We cannot help thinking metaphorically – that is how we are made – but we can reflect on it. We should do so, at the least, whenever we are asked to turn into poodles, get up from our chairs or strike anything.