Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
underlay, underlie (vv.)
These verbs contrast and pose usage problems exactly as do lay and lie (which see). The principal parts are underlay, underlaid, underlaid for the transitive underlay (We underlaid the siding with an insulating board), and underlie, underlay, underlain for the intransitive underlie (It is supposed efficiently to underlie any sort of siding).
