But when does it cease to be that? When do you start hoping he won't be home so you can bring a trick back? When do you start saying: 'Got another arts do on tonight. You won't want to come, will you?' When do you start slipping sideways into bushes at Russell Square after every social engagement?

How long is it then before there is no sexual side to the marriage? What do you call the marriage then? Like other mainly financial arrangements, you might call it a partnership. They still both took a measure of pride in it.

'He's a scientist,' Phil said at a recent party, as if clearing the table for a specially cooked, nut-free dish. Philip at 31 was already beginning to look ragged and discontent. 'He's doing brain research. You're trying to prove we have a soul aren't you?'

'Do we have a soul then?' asked Jimmy Banter. He was a better-known artist than Philip. He had a merry smile and a watchful eye.

'What we have,' said Michael, feeling his weight, 'is more like a centre of gravity. You can't find a centre of gravity surgically. It's not an organ or an inner eye. You won't find a car part called the centre of gravity, but the car has one anyway. The self is like that. It's the centre of focus if you like, where all the stresses and strains of the brain come together.'

Jimmy Banter looked over his shoulder. 'Is that why you've got such a big ego then, Phil? All those stresses and strains?' Jimmy disliked weight and he disliked bald truth but he loved drama.

'At least my work doesn't involve killing chickens,' said Philip.

Thanks, Phil, for blowing my cover.

The room went cold and still. 'What was that?' a woman in a red dress asked, sitting up.

Michael sighed. 'Uh. I am about to start a research project that involves experimentation on animals.'

'And how,' the woman asked him, with the cautious determination of the righteous, 'do you justify that?'

With difficulty. It takes a long time. Most of the night, in fact. And the one thing I dread is some animal rights activist getting hold of it because my partner wants to score points at parties.