As a result of observations made over many, many years, physicists have inferred that: "No experimental test provides any way to distinguish an inertial frame from another." This negative form of the statement is important, as it is a prediction which can be tested experimentally and thus falsiﬁed. It has never been. I have been unable to undestand why the negative form of the statement is important. So, I have attempted to write down the positive form of the statement. This is it: "There is an experimental test that can distinguish between inertial frames." This is not a prediction (as it does not follow from the experimental evidence of the last four hundred years), but the statement can be put to test through experiments. However, it will be very difficult to prove as all the experiments conducted so far have been unable to distinguish between inertial frames. So, the matter would remain inconclusive. In spite of what I have written, I still don't understand the importance of writing down the prediction in a form in which it can be falsified. Any ideas?