historically, i.e. speaking philosophically, only things known a priori can be considered facts. if the knowledge is arrived at by experiment, we have to defer

historically, i.e. speaking philosophically, only things known a priori can be considered facts. if the knowledge is arrived at by experiment, we have to defer to the quality of our senses (or the senses of our measuring instruments). not feeling the heat (or our measuring instruments not picking them up) doesn't mean heat is produced by certain activities. seen this way, what you'd call facts after rigorous experiments is essentially the perspective of the observer and the quality of our measuring tools at this point in time. as both improve, new facts will be observed. then what happens to the old fact? no longer facts? if so, why were they called facts to begin with? the word fact derives from the latin factum. immutability is conferred since factum implies that the event has been sealed by time. if it's bound to change, let's call it something else, shall we?