This is the sort of truth that we can find in pictures, novels or films. We are not saying that what we are looking at, reading or watching is actually true. However, we might say that it is 'true to life'. By this we mean that it is believable - it could happen - although it is not actually true itself.
This is quite straightforward. We can say that we 'know' that something happened in the past even though we were not there and did not see it for ourselves. We know that it happened because we have seen evidence, such as archaeological or films or documents, and from this evidence we can know that certain things happened.
When we talk about moral truth we mean that we 'know' that something is right or wrong. This is almost like an instinct. We know that it is wrong to steal or to kill people. We…