Knowledge lies in the realization of truth.
It is within one’s own self that true knowledge may exist, though this can only be gained from paying attention to the external world. This is for the innate nature of knowledge being truth, and truth being something totally relative. In the words of Descartes, “cogito ergo sum,” I think therefore I am. The truth of this phrase is the knowledge that, though other things may appear to be true, the only truth that we can know without a doubt is that we, as a entity that experiences thought, must exist. This is as our senses may be deceived. By avoiding the clouding of ego, it must also be concluded that other thinking beings also exist, for without this, we are the only existant force, simply manifesting a dream of reality. So, we exist and so must others.
The issue, I think, with the logic that we cannot at all, trust our senses, is in the face of the true loneliness and lack of information it affords us; for as it can be seen, from this truth no more truth can be attained. It is therefore so, that we must assume that objective truth does exist beyond this realm of self and by joining the knowledge of our senses and the remembrances of others, we can hope to eventually reach that objective truth.
And so, comes science into our little worlds. Fundamentally science follows the philosophy that truth exists and to further our knowledge of this we must theorise, experiment and disprove previous knowledge. It is that the truth of our senses and what can be observed is the overarching truth, and that anything theorised is true until proven otherwise.
The assumption of science, that truth does exist beyond the realm of self is the only way to allow oneself to advance within our shared reality. Only by combining the observations of many can we then come to a shared realization. Be that realization, the ideal temperature for baking bread, or the basis of quantum mechanical systems, it is through sharing knowledge and refuting falsehoods that we reach truth.
As for my actual belief on the topic. I believe truth is a totally relative concept and that it may be different for every individual. However I also find that the most effective path is to follow the assumption that objective truth exists and also that others may have knowledge of a different part of this truth. Therefore to have an effective relative truth is to have transferred as much knowledge in and out from other sources and therefore containing within our knowledge an approximation of objective truth.