1
general::
The fundamentals of education, as in It's a terrible school; the children are not even taught the three R's. It is widely believed that Sir William Curtis, an alderman who became Lord Mayor of London, once presented a toast to the three R's?? reading, riting, and rithmeticthereby betraying his illiteracy. In any event, the term was picked up by others and so used from the early 1800s on.
American Heritage Idioms