I snowboard a bit. Every couple of years I hit the slopes, pick up where I left off and get a little better. What I learned in my first few goes is that you get the furthest by making only small course corrections. Left to your instincts, the fear of gathering too much speed makes you want to fully control each turn, to absorb all the momentum so that you can gather your thoughts before initiating the next turn.This is a terrible approach, since the act of making safe often makes you wobble and fall – most rookie wipeouts are due to this fearful overcompensation. The same effect occurs in early stand-up gigs by the way. Hold the course and all will be well; check in compulsively with how the gig is going and you will project doubt, sending the value of your stock into a tailspin. Credit checks harm your credit rating.Democratic societies also slalom forwards, tacking to the political left and right as they progress. But they also trend leftwards or rightwards across the mountainside: the political centre is not a fixed place on the mountain but the midpoint of the skiers on the slope. What was left wing in the 1970’s is extreme left wing now, for the centre has drifted rightwards since the 1980s, when Thatcher skidded sharply to the right and then Blair, pragmatically, followed to within hailing distance, always staying within the Overton Window.From extras.I like to drop the Overton Window into conversation whenever I can – my opportunity to do this I call the Overton Window Window. But since you ask, the Overton Window refers to the visible spectrum of ideas tolerated in public discourse, ranging in their political acceptability from actual policy outwards through popular, sensible, acceptable, radical and unthinkable. Politicians who wish to be elected or to remain in office are advised to keep their policy proposals within this range – and over time the range itself is nudged left or right: radical ideas become acceptable, sensible and then policy.Our parliamentary system of debate is supposed to illuminate this spectrum of opinion. It should work like a courtroom: each side must present its arguments as vigorously as possible, averaging out everybody’s bias and leaving the truths exposed. It is a system that works well at keeping our society on a reasonably even keel – as long as everybody shows up to do their bit in the adversarial process. When, however, one side fails to attend the debate, as in the history-making case of the Remain campaign that never was, the snowboard can lurch unpredictably. Leaving the EU rather than remaining in it and reforming it procedurally will be such a lurch – not leftwards but towards nationalism.When extreme parties gather grassroots support, they tend of course to siphon it from their ideological near neighbours. To win those votes back, moderate parties can be tempted to tack to the extreme. This risks losing votes from their centrist flank – so they prefer to stay where they are and emit a series of ultrasonic pheeps audible only to the pricked ears of the hardliners, signalling to them that their sympathies are really with them, but that the shills in the mainstream won’t let them say so. It is fair to say that Cameron did not deftly pull this off.