ABSTRACT
"The earth is round" is a surmise or conjecture about certain facts, i.e. a factual hypothesis—or a hypothesis in the epistemological sense. Hypotheses, indispensable in rational action, are even more central in the rational conception of the world and in its rational modification. In the logical sense of 'hypothesis' all the initial assumptions of a theory, whether formal or factual, are hypotheses; they are distinguished from the remaining hypotheses of a theory by being called fundamental or basic hypotheses. Factual hypotheses are surmises formulated to account for facts whether experienced or not. In science, several main requisites for the formulation of hypotheses are imposed. The task of founding scientific hypotheses on grounds other than empirical evidence may be called their theoretical justification. Scientific hypotheses are all more or less grounded on previous knowledge, i.e. they are advanced, investigated, and entertained on definite grounds other than the data they cover. Corroborated hypotheses, well-grounded and empirically confirmed hypotheses.
