All beliefs as to simple matter of fact must rest ultimately on observation. But, of course, we believe many things to have happened that we have never seen. As Chaucer says:—
But God forbedë but men shouldë 'lieve
Wel morë thing than men han seen with eye.
Man shall not weenen everything a lie
But if himself it seeth or elsë doth.
For the great bulk of matters of fact that we believe we are necessarily dependent on the observations of others. And if we are to apply scientific method to the ascertainment of this, we must know what errors we are liable to in our recollections of what we have ourselves witnessed, and what errors are apt to arise in the tradition of what purports to be the evidence of eye-witnesses.
I.—Personal Observation.
It is hard to convince anybody that he cannot trust implicitly to his memory of what he has himself seen. We are ready enough to believe that others may be deceived: but not our own senses. Seeing is believing. It is well, however, that we should realise that all observation is fallible, even our own.
Three great besetting fallacies or tendencies to error may be specified:—
1. Liability to have the attention fastened on special incidents, and so diverted from other parts of the occurrence.