This question has come up several times here, and I'd like to make it clearer with an example. Imagine that Pontius Pilate had written his memoirs, and that those memoirs had come down to us. Imagine also that he had once had a best friend named Marcus and a dog named Macula.

If Macula once bit Marcus, it would be understandable if PP chose not to record that event, because that would not be fundamentally unusual. But if Marcus had once bit Macula, then I'm sure that PP would have wanted to record that event.

So it is in that light that we ought to evaluate arguments from silence. Is the event some ordinary one that the historians in question would not have thought worth talking about (Macula biting Marcus)? Or is it some bizarre one that the historians would have recorded if it had happened (Marcus biting Macula)?

Though IMO this is a reasonably good criterion, it may still fail. For example, the supernova of 1066, which produced the Crab Nebula, was recorded in China but not in Europe. Nobody knows why this "guest star", to use the Chinese chroniclers' term, was not recorded in Europe; the best guess I've seen was that it was considered some extremely perplexing evil omen.

Sorry, I goofed. That supernova had been in 1054.

Suppose Pontius Pilate wrote a memoir and made no mention of his dog at all. Would we be justified in thinking he had one? I mean, it's not like he comes out and says, "I never had a dog."