I've recently joined a discussion in which some of the participants insist that if one doesn't understand the nature of the difference between two or more words (the ones discussed by us are synonyms or near-synonyms, but it could be a more general problem) at a particular synchronic level, they can resort to etymology to figure it out.
I have expressed my doubts, because I don't believe etymology can do that. I believe etymology can be used to explain how such differences may have arisen, but if we actually want to grasp them at all, we need to study their synchronic properties in synchronic contexts.
Can somebody possibly provide me with some arguments (and/or examples) that could either confirm or refute my opinion?
So far, I've only been able to come up with the imperfect example of English 'arm' and Czech 'rameno': If we only knew the meaning of the Proto-Indo-European root they both come from, but didn't know their current meanings, we wouldn't be able to determine those meanings, would we? There would be no way of knowing that the latter actually means 'shoulder' in contemporary Czech, not 'arm' (and vice versa). Only after we have learnt their current meanings could we use etymology to explain how the differences may have come into being, am I right?
Many thanks for any ideas!