Whenever a Commons vote is described as "nip and tuck" or "too close to call" the advantage is almost always given to the government.
Tuition fees may just be about to blow that traditional certainty out of the water.
Student fees vote looks likely to go to the wire
Even a random survey of the two sides in the debate suggest that, this time, the vote really could go either way.
The rebels believe their core vote is rock solid and that it may still be enough to defeat the prime minister.
Leading rebel Dr Ian Gibson said the crunch issue was still variability and that was "non-negotiable".
Supporters, on the other hand, believe the campaign of persuasion and offering concessions have probably done enough to secure victory.
Reading MP Martin Salter said it would be sensible to vote with the government rather than go into the voting lobbies with the Tories.
But a new factor has been thrown into the equation following comments from Chancellor Gordon Brown at the weekend which some have seen as a suggestion Tony Blair may be ready to stand down sooner rather than later.
Mr Brown said it was a matter for the prime minister whether he was still in post at the next election.
Brown has renewed speculation
That has stirred up all the old speculation that the two have done a fresh deal to hand over the succession to Mr Brown.
And the prospect of bringing down the prime minister has certainly appeared to have swayed some rebels, as have suggestions the vote is being used by some of his fiercest critics to finish him off.
Hints that Mr Blair may be ready to stand down anyway might release some rebels from any feelings of guilt if they defeat him on Tuesday.
But the majority of backbench MPs do appear to be taking positions based on their own beliefs and, perhaps more importantly, their constituency parties.
One rebel, Peterborough MP Helen Clark, said she had been following what she believed was government policy when she told her local activists she was against fees.
It was impossible for her to now execute a U turn.
Tuesday night still looks set to be the most edge-of-the-seat vote seen in the Commons for years.
And former minister Frank Dobson said it was "very, very close" and he claimed that a lot of rebels who were opposed to different aspects of government policy had rallied around the tip up fees vote.
But Mr Salter, who originally signed the rebel motion, said he was not about to help the Tories defeat Mr Blair.
In all these things, as one backbencher told BBC News Online, "there's always a good 10% to 15% of those you talk to who are telling you lies".
So making predictions is a bit of a mug's game, particularly only a matter of hours before the crucial vote.
But Tuesday night still looks set to be the most edge-of-the-seat vote seen in the Commons for years.