defendant were speaking the truth, there was no way that the Police could have got on the track of the second defendant when they did, unless he had been involved in the offence and had been betrayed by a third man, whom everyone agreed had been involved. Similarly, when I had cross-examined the second defendant about his movements, I was able to submit that if he were speaking the truth, there was no way the Police could have got on the track of the first defendant, unless he had been involved and had been similarly betrayed. The point was that, whilst each defendant was concerned to cover his own traces, he had no time to think of his fellow. Fortunately there was a break, I think lunch, between the two cross-examinations. Of course I had conceived the idea beforehand of asking each to compromise the other, but the actual mechanism of doing so had to be devised on my feet, which was not easy. I was lucky to have the lunch break. Unfortunately the judge made a mistake in one part of the summing up, and the conviction of one was quashed on appeal. But unless one can switch one's sense of perspective, one's cross-examination is little better than saying, “I put it to you that you did it”, which gets nowhere.
This then is the fallacy in Laplace's hypothesis, because he assumed that the man, whom the mathematician was observing, had a fixed settled outlook on life. No-one has in practice, except in the face of death. Everyone to a greater or lesser degree, when they are weighing up the pros and the cons, so as to arrive at a judgment of value, and a decision as to what to do, shifts his outlook a little this way and that. Of course Laplace would say, “Yes, but these attitudes are also themselves predetermined by past experience”; and to some extent that must be true. But taking the law courts as an example, the fact that one's view of what is likely to happen is largely moulded by past experience, so far from being a hindrance, is a great help in reaching the correct decision on the particular occasion. Indeed, this is the correct use of experience: to let it mould…