Jamie 
Some think knowledge is a belief which is always true. They might say, “I know the sun will come up tomorrow.” But, such a statement would prove false in the aftermath of a supernova. We can overcome this difficulty by eliminating the prediction and focusing on the present, saying instead, “The sun came up today.” But did the speaker directly observe the sunrise? Or did they figure because the sun is in the sky it must have risen. What about days where it is light out, but clouds obscure the sun from view. We assume the sun is behind the clouds without actually seeing it.
Even when the statement is narrowed to the sun came up this morning, and I know this because I saw it rise, many other questions such as where you where located come into play. Is there a sunrise at the North pole? Requiring all knowledge to be the result of personal experience is very limiting. Moreover, studies have shown eyewitness accounts are often incorrect or misremembered. These findings can shake a persons faith in anyones ability to know anything.
This kind of dialog is what often irritates new students of philosophy. The seemingly endless questioning and doubting lead them to wonder why anyone should care about epistemology?
Rather than insist a belief must be universally true, we look at what is a reasonable justification. Things like “the sun will come up tomorrow” are common to human experience. Often referred to as common knowledge, such statements require little effort to convince others of their accuracy.
The problem of requiring knowledge to be always true extends to science. Newtonian mechanics made way for the theory of relativity. Yet today Newton’s theory is still taught as knowledge with the caveat that it works except in unusual situations such as moving very close to the speed of light. Relativity covers the extreme cases, but predicts the same outcomes as Newtonian mechanics for the usual conditions encountered.
Science uses a systematic approach to test validity. Repeatable experiments with measurements and objective observations are relied upon by a community of practitioners searching to understand phenomenon. Results are analyzed and the conclusions questioned and debated. Ultimately, scientists become convinced and accept the validity of the findings. This process like most involving people is a bit chaotic. Egos can challenged and tested. Mistakes and errors do occur while participants struggle and hope optimistically the truth will ultimately prevail.
For us at Research on Knowing, the key question is what evidence justifies holding that a belief is valid.
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