What's the real reason to hold an EU referendum?
What's a Europe referendum for? Does that sound like a silly question?
Surely, you might say, it's obvious that a referendum is for giving the public a say on Britain's future in Europe.
Well, no, actually.
Some want a referendum because they think the people will do what no mainstream political leader dare - get us out.
Others - who want the UK to stay in Europe - want a vote to put pressure on Europe's politicians to give the UK what it wants.
Many Eurosceptics - both those who want to stay in and those who would sooner get out - believe it will put pressure on a British government to negotiate harder.
Most Tories hope that, whatever the vote is on, the promise of a referendum will help them see off UKIP.
A growing number of Conservatives believe, as Harold Wilson did in 1975, that a referendum is the only way of stopping their party splitting on the issue of Europe.
Very few, in my experience, simply want to know what the public thinks.
PS David Cameron and Liam Fox appear to be contemplating the same sort of referendum - a post renegotiation poll. What separates them is that the prime minister is clear that Britain needs to stay in whereas his former defence secretary is now ready to contemplate getting out. That's the divide that really matters.