Today is Valentine’s Day, so it’s appropriate that the big release is a romantic comedy. Not that we don’t get a steady stream of them all year long, but Two Weeks Notice (its makers dropped the apostrophe, not I) is a rather superior example of the genre. Romantic comedies need two elements: one, chemistry between the leads, and, two, ways in which the predestined union can be delayed for an hour and a half. We know the two leads will achieve a final happy union, but if there are no obstacles en route to this climax there’s no movie. Delay is essential. It’s rather like a sex manual’s instructions on avoiding premature ejaculation.As for the first element, Hugh Grant and Sandra Bullock luckily do have that chemistry. Both are accomplished players with firm filmic personae; neither are going to surprise us by subsuming themselves in an unexpected character. And they are a good combination: Grant has that diffident, slightly effete British charm, while Bullock is clearly a girl with balls.As for the second essential element of romantic comedy (the delay), this is dealt with by making the two lead characters innately opposed. Grant is a ruthless, amoral property developer; Bullock is a feisty lawyer given to socially conscious causes. At first she fights him, then she gets employed by him — and finds herself still fighting. From there things develop in a predictable but amusing direction. The underlying plot here is that of good woman reforms immature man, which, as we know, is a real no-hoper in real life, but here it provides a satisfying story trajectory.Of course it’s absurd, and of course it’s sentimental, but the joke quota is higher than average in Two Weeks Notice, which makes all the difference. Bullock is generally the straight man and Grant the funny man: he has a highly competent way with a dry one-liner, though he also has a tendency to mug rather too easily, and, in Richard Gere fashion, his eyes seem to be growing smaller and closer together with each movie he makes.Two Weeks Notice being entirely sex-free, I had hoped Investigating Sex would provide a counterbalance. It’s about a group of artistic and academic oddballs in the Twenties exploring the nature of sexuality — by talking about it, of course. Actually doing anything is initially not on the agenda, but what eventually happens is as predictable as the romantic union of Two Weeks Notice.The idea of Investigating Sex is interesting (it’s based on the Surrealists’ Récherche sur la sexualité) and could perhaps have made a watchable playlet. As it stands, it suffers from a fatal confusion: its supposed mockery of pretension is indistinguishable from pretension itself. That is to say, it thinks it’s a funny, sophisticated, meaningful movie, and the actors (among them the estimable Dermot Mulroney, Alan Cummings and John Light) keep gurning along enthusiastically under that misapprehension. How wrong they are. A couple of their co-stars, perhaps wisely, do not appear to be taking this very seriously at all: Tuesday Weld has an accent that veers alarmingly between Berlin and Brooklyn, and Nick Nolte seems thoroughly sozzled in at least one scene, though that may just be method acting.