David Cameron says air strikes against Islamic State militants in Syria would be in our national interest, but it is hard not to feel profoundly uneasy when a British Prime Minister stands up in the Commons and says there is a solid case for war. We have been here several times before, with disastrous consequences, and David Cameron knows it, which is why he is trying a different strategy by insisting there will be a plan for the peace as well as the war.

But how much further forward are we really after the Commons statement? The Prime Minister says he has a seven-point plan which includes air strikes, counter-terrorism measures, and a plan to reconstruct Syria after the conflict. But in the Commons the Labour leader Jeremy Corbyn responded with seven questions, including whether the Prime Minister believes air strikes will make a significant military impact. He also asked whether British grounds forces would be deployed and in what way air strikes would contribute to a long-term political settlement.

All of these questions are fair and to the point, but the argument about air strikes and their aftermath can be boiled down even further to three essential questions. Why should we launch military action? How would it be done? And, what would come afterwards?

On the first question, why should we launch military action, there is a large degree of consensus. Twelve years ago, Tony Blair made the case for war in Iraq on an unfounded claim of weapons of mass destruction, but the threat we face now is in a different league, with Mr Corbyn saying there is no doubt that IS pose a threat to the British people. But the threat does not necessarily lead to a military response because the fear is that if IS militants are going to strike the UK, they will do it anyway – after all, thousands of airstrikes have been launched since August 2014 and yet the murderers still struck in Paris. And the even greater fear is that any military action will actually increase the risk, not reduce it.

The second question is: what form would military action take and on this the Prime Minister favours air strikes and has ruled out ground forces. But what is the point of that? Senior figures in the military have repeatedly said bombing from the air alone will not defeat Islamic State and there is already a problem of finding targets to hit. Would British participation add anything significant that is not already being done by the US, France and our other allies?

The issue of ground forces is also clouded in doubt. A secure future for Syria will not be found without them, but, mostly because of the long shadow of Iraq and Afghanistan, the Prime Minister has ruled them out. Who will provide the ground forces when they are called for? Mr Cameron says there are 70,000 anti-Assad fighters who could be used, but are there really that many? And even if there are, they have proved largely ineffective so far. And what would ground forces do anyway? Would their mission be to remove al-Assad, or keep him in power? It is unanswered questions like those that mean a repeat of the disasters of Iraq and Afghanistan is possible.

The final, and in many ways most important, question is: what would come after military action? The Prime Minister says he will advance a political settlement but it is unlikely it would tackle the central issues such as the Middle Eastern states that support IS. And what about the financing of IS, through the arms trade and stolen oil? There is also the grim reality that no one predicted the rise of IS and no one can predict what might come after it were it destroyed. As Jeremy Corbyn suggested in the Commons, even if the air campaign was successful, it is likely that other, stronger jihadists would simply take over where IS left off. There is also a real danger that the migration crisis would worsen.

Will any of Mr Cameron's answers to these questions convince the Commons? The SNP has already said that, for them, the key questions on Syria remained unanswered, which means that with the nationalists unlikely to support air strikes, Labour holds the key to the Prime Minister's success in winning the vote. The problem is that the party is split so the result is hard to predict although it appears that many are supportive. The vote may well go the Prime Minister's way but if it does, it will do so while some of the key questions about military action against Syria remained unanswered.