This is true, though empirical findings often cause paradigm shifts that could not be explained by prior philosophies, and so a new philosophy must be written to explain the findings. It is in cases like this that science and philosophy feed each other. The basic assumptions weren't asserted out of nowhere, but were based on inferences on empirical findings. These inferences were sometimes wrong and so we had to reject those assumptions as we got more data, but that also shows the empirical foundations of the basic assumptions.