The contradictories, ie, entities and qualities that have some difference between them, can be: contraries, semi-contraries or collaterals. The collaterality - the term is mine, in the field of dialectics - is, therefore, the minimum difference while the contrariety (black versus white, lion vs zebra, revolutionary proletariat versus bourgeoisie, for example) is the maximum difference. Empiricism is contrary to idealism? No. David Hume was an empiricist and idealist - something that analytic philosophers are unable to conceive due to the cloud of confusion within it they vegetate.
In fact, the Routledge Dictionary of Philosophy, exposing the standpoint of analytical philosophy, does not classify David Hume as an idealist but only as empiricist:
«Hume, David, 1711-76. Scotish, born in Edinburgh, and generally regarded as the greatest of "British empiricists" (...) This led him to generally skeptical conclusions about such notions as REASON, CAUSATION and necessity...» (Michael Proudfoot, A.R. Lacey, Routledge Dictionary of Philosophy, Fourth Edition, page 169)
In this Dictionary there is not a single reference to the idealism of Hume. But, in fact, Hume is an idealist: he suppresses the reality of matter in itself.
Then, what is the relationship between empiricism and idealism? It is a relationship of collaterality. There is a realistic empiricism, an idealist empiricism and a phenomenological empiricism. This is the same ontological empiricism added of different pedestals: the real matter (realism), the unreal matter (idealism), the problematic matter(phenomenology).
© (Direitos de autor para Francisco Limpo de Faria Queiroz)