It is as though the whole network of structural relationship between forms, overlapping sometimes into the non speech context, constituted a complex intertwining of various kinds of valences, only one layer of which is immediately apparent to the analyst. This most apparent layer constitutes, we shall say, ‘surface grammar’. Beneath it lie various layers of ‘deep grammar’, which have much to do with how we speak and understand but which are still largely unexplored, in any systematic way, by grammarians.
- Hockett (1958), Pag. 249