You can only believe in what you know to be true

What relevance does this statement have to scientific thought, what could be a possible argument against this idea and what other factors can influence scientific belief?

Thank you so much for all your help and i swear after i have finsihed my BMAT i will stop posting annoying questions xXx

This is quite a tricky issue and needs some teasing apart.

The place to start looking at this statement is 'know to be true'. A person might believe they know something to be true simply because they have never questioned it, have been told it by somebody they trust, or read it in a book which is generally taken to be an authoritive source.

None of these are cases where the person knows for themselves the truth of the statements. Probably most people will accept that there is a planet called Neptune, but few people have seen it. Even the ones who have seen the stunning photographs of it are not in a position to check the veracity of the photographs. They believe in the existence of Nepture, but in what sense do they know it to be true?

So it is perhaps more true to say that we believe in what we believe we know.

In principle the whole edifice of science is based on sound observation, clear definition, rigorous logic, rational theorising and hypothesis testing. This is the hallmark by which a scientist knows something to be true, and is thus something that confidence can be placed in. Even then what you have is simply the best current working hypothesis (classic case being Einsteinian physics refining and reinterpreting Newtonian physics). Science is what scientific process verifies, not simply what a scientist says, so what you know to be true is always an ongoing process of refinement.