Some statements are entirely about observation. An uncompromising empiricist might say that these statements alone are meaningful; but in that case, theoretical science shares in the downfall that was meant for metaphysics. An uncompromising empiricist might tough it out: science is indeed meaningless, but yields meaningful theorems; or it is entirely about observation, after all; or some of each. But it seems, rather, that science is partly about observation and what we can observe, and partly about the hidden causes and minute parts of what we can observe. And it seems also that science is a package deal, which cannot credibly be split into one part that is meaningful and one part that isn't.

The sensible empiricist, therefore, will retreat. Statements entirely about observation may remain at the core of the meaningful, but scientific statements also will be admitted. Collectively, and even individually, these are at least partly about observation. For an empiricist who wants to be a friend to science, that had better be good enough.

One empiricist who sought to eliminate metaphysics but spare science was A.J. Ayer. Meaningful statements need not be entirely about observation.

Dissatisfied with this use of the notion of evidential relevance, he offers a ‘clearer’ formulation.