alt Hacker Newseh, momentum has a pretty rigorous definition and it's possible to define it qualitatively. perhaps a better example would have been hardness, where A is harder than B when it scratches B in a test. but it's borderline, and quite a bit different from true circular reasoning
test X measures I(x) I(x) is defined as the thing test X measures. Therefore test X measures the pre-existing psychological trait intelligence.
this is absurd
There was no pre-existing trait called intelligence to measure.
The was just a vague idea that some people might have a bit more of some underspecified general quality but there never was any good idea what exactly that might be. So making a test that measures something correlated with outcomes that people associate with this nebulous pre-existing idea of intelligence is honest and fair stab at something that eluded our grasp for millennia.
Intelligence as people were talking about it before we created intelligence tests is something like atoms of Democritus. And IQs are atoms as we mesured them today.