There are lots of possible factors, and opinions will differ as to the order of priorities. However, this is one possible list:

1. How strongly do you really feel on this issue? Strongly enough to risk your future career? If so, you will vote against the measure, whatever the consequences.

2. Let's say, for the sake of argument, that you care very deeply but do not want to throw away your career. So the first factor would probably be the possibility that your party will resign if it loses the vote. Remember, the media is very interested in the issue, but we haven't been told why. If it is because the government's existence is a stake, you might not want to be on the opposite side in such a crucial division.

3. If your party is likely to lose, is the vote going to be close? Will your decision make a crucial difference to the survival of the government? If you are just one of numerous rebels, even if your party loses office you are more likely to be forgiven rather than discussed in the media as one of the handful of people who brought down your own government. On the other hand, in a close vote you could win a promise of early career advancement, provided that you play your cards right.

Does your party have a tradition of dealing harshly with rebels? How good is your relationship with other members of the party – especially its leaders? You have never been disloyal before: that much we do know. This will probably count for something, especially if you are one of a large number of 'rebels'. Even if a government defeat will lead to a setback in your career, with the goodwill of the party behind you this could turn out to be a temporary setback.

4. How large was your majority at the previous election? How much did your victory depend on personal popularity, or did you just win a seat where your party is invariably victorious? If you have won only a narrow majority in an election which your party won overall, the idea of standing as an independent in a future contest will make limited appeal. However, if you are very popular locally this might be a viable option.

5. What is the balance of opinion in your constituency on this issue? Do lots of people feel as strongly as you do? If so, even if you weren't very popular before – remember, your views on this subject had never previously been expressed – there is a chance that you could cling on to the seat at the next election, even if your party denounced you and you were forced to stand as an independent.

6. How proficient are you in broadcast interviews? If you are unusually skilful, you could win a nationwide reputation from the publicity arising from this event. If so, other constituencies might want to adopt you as an independent candidate, with a reasonable chance of winning.

7. How have other parties voted on the issue? Is there a powerful party which disagrees with you on most other subjects, but agrees with you on this one? If so, you might consider the option of defecting.

There are several implications of this particular list. First, it is normally very difficult for members of a legislature to vote in accordance with their consciences when these dictate a vote against their chosen parties. Second, if the moral commitment is either very strong or fairly weak, the decision is relatively easy: if very strong you will vote against this proposition regardless of the consequences, and if fairly weak you will support your party. The problem arises for legislators in the middle of the spectrum. Their decisions can be affected by a very wide range of factors. Note also that the views of constituents come into play towards the end of the list, not at the top as they would do in an 'ideal' representative democracy.