Must You See To Believe?

One is taught in school (and elsewhere) the importance of the dictum Seeing is Believing, and quite rightly so, for that dictum acts as a protective shield against the wiles and the treacheries of swindlers, sophists, punsters, and ironists. However, does it imply that if you cannot see something with your own physical eyes you should disbelieve in its existence? Consider the following list of ‘things’ : the moons of Jupiter, the thyroid gland in your own body, the duodenum of your friend, a positron, Stockholm, a string of DNA, and a neutrino. I take it that you, the reader of this blog, have not seen at least one of these entities --- I myself have not seen any of them. Why do we nevertheless believe that they exist? Perhaps we have an astronomer friend who has told us that Jupiter does have moons; or a geneticist cousin who has seen the structure of DNA with her own eyes; or a friend who spent the last summer in Stockholm; or a physicist flat-mate who has given us arguments in favour of the existence of the positron. In all these cases, we implicitly trust these people, we trust that they are not deliberately trying to mislead us, and that they have indeed seen one or the other of the above things with their own eyes.

Therefore, if we were to accept the claim Do not believe in what you have not seen with your own eyes and follow it in a rigorous and consistent manner in our lives, we would very soon pile up a list of hundreds of things in whose existence we must either disbelieve or about whose existence we must exercise a complete suspension of judgement.

At this stage of the argument, however, an interesting question comes up : how shall we know in whom to place our implicit (or even explicit) trust?