Feynman argues that scientific knowledge is ultimately tested against experiment rather than accepted on the basis of authority, elegance or established theory. A scientific explanation may be mathematically convincing or widely supported, but it remains subject to observation. If experimental results consistently conflict with a theory, the theory must be revised or rejected.

The wider passage also stresses that scientific knowledge is provisional. Feynman presents existing explanations as approximations that can be corrected as new evidence becomes available. In this sense, experiment is not simply a way of confirming what scientists already believe; it is the means by which those beliefs are challenged and refined. The quotation therefore expresses a central principle of the scientific method while also raising an epistemological point: reliable knowledge depends on a willingness to test claims against reality and to change conclusions when the evidence requires it.

Full quotation

“Each piece, or part, of the whole of nature is always merely an approximation to the complete truth, or the complete truth so far as we know it. In fact, everything we know is only some kind of approximation, because we know that we do not know all the laws as yet. Therefore, things must be learned only to be unlearned again or, more likely, to be corrected.

The principle of science, the definition, almost, is the following: The test of all knowledge is experiment. Experiment is the sole judge of scientific truth.”