Middle East Editor, BBC News
Here's a dilemma of modern life. When is it permissible for armed forces to attack a hospital? Never? Sometimes? When it's necessary? If so, who decides what is necessary and what isn't?
One of the problems with spending a lot of time recording the bad and vicious things that happen in the world is that after a while you need a measurement of how bad and vicious they are, and why they are like that.
How far does the right to self-defence go in armed conflict?
Commanders who launch attacks will always have some way of justifying what they do.
These days, "national security" or "fighting terror" are popular ones. So is "resistance". Anyone who questions those justifications can find him or herself consigned to the bin marked "enemy".
People who are concerned about what might be happening in their name, should pick up a book by Roy Gutman called Crimes of War: What the Public Should Know.
The latest edition has just been published. It was conceived, first of all, as a handbook for journalists, but anyone who is interested in what is happening in the world ought to read it.
Every imaginable war crime
It lists, in alphabetical order, about every war crime you can think of, and also has case studies of some controversial theatres of war crime - like Cambodia, Congo, Colombia, Iraq, and the Arab-Israeli wars.
It is illustrated with the work of some of the best photo journalists.
It is easy to be cynical about the laws of war. After all, they are often broken - by small bands of insurgents and by big powers
The crimes are written about not just by lawyers, but by reporters who have witnessed them happening.
To declare an interest, I contributed a small section (two pages out of more than 400) on the crime of wanton destruction during the war in Chechnya in the winter of 1994-95.
It is easy to be cynical about the laws of war. After all, they are often broken - by small bands of insurgents and by big powers.
Since 11 September 2001, the United States has turned its back on important parts of the Geneva Conventions.
I was as cynical as anyone else when I started working in violent parts of the world.
I reckoned that the strong were going to prevail, and in wars they would do what they thought was necessary to make sure they won.
But after I had seen a lot of bad and vicious things happening, I realised that - even when they were broken - the laws of war were the measuring stick I needed in order to make a proper assessment of what was happening.
The main thing that lifts journalists in wars above the level of voyeurs is the obligation to bear witness to what they see
Not all of our audiences would agree, but here at BBC News we try very hard to be impartial.
I think knowing something about the laws of war (and knowing where to look them up) is an important part of that.
It is a bit unreasonable to allege bias if a story about the conduct of war is based on whether an attack breaks the law or not.
The main thing that lifts journalists in wars above the level of voyeurs is the obligation to bear witness to what they see.
That principle is not usually meant in its legal sense, but if you know what the law says, the job gets easier.
Principles of war
When a reporter is in a city under attack, full of rubble and fear, it is hard enough to find out what is happening.
But it is not impossible to use your own eyes to work out whether the damage and death that is being inflicted is in proportion to what is going back in the opposite direction.
Viewers, listeners and readers can do it too. Start by remembering the principle of proportionality.
My copy of Crime of War reminds me that the use of force by a state in self-defence must be necessary and aimed at neutralising the attack it is facing.
The other obligation is to make sure that attacks, even ones that are legitimate and in self-defence, do not cause disproportionate loss of civilian life or damage to civilian objects.
And as for whether it is okay attack a hospital, the short version is that hospitals are protected by the law, and so are the people who work in them.
But it is also unlawful to use hospitals, or ambulances, as shields for the military.
Collateral damage to hospitals that comes from attacks on legitimate military targets is not necessarily unlawful.
For the full answer turn to page 220 of Crimes of War, or look at