When I was learning English, “Substitute X for Y” meant that Y was the standard and X would be the substitute. About ten years ago, newspaper cooking columns started to use it to mean the opposite – in a brandy cake you could “substitute brandy for your favourite liqueur.” They ignored pedantic attempts to get them to change their ways. (Hey, I teach small children: pedant by definition…)
Now a spokesman says that the National Heart Foundation guidelines recommend that we “substitute saturated for polyunsaturated…” From context, I am sure that he meant the opposite. (27.30 on http://www.abc.net.au/catalyst/stories/3876219.htm )
Thought:
Many dictionary-linguists have trained through Anthropology, and use its emphasis on cultural relativism – report what is done, do not make value judgements on others’ ways of being. They push for dictionary definitions and grammatical texts to reflect current usage (“…it means just what I choose it to mean,” said Humpty.)
We teach literacy with concern for the transmission and reception of ideas. How do we balance the push to Humpty with the need to transmit thought clearly across age groups, nations, and centuries?
Erasmid 