This is not an introduction to the subject of linguistic form, but a brief commentary on current views and terminologies.
If it is possible to discover any aim common to all linguistic schools, this aim is the reduction, by terminological devices, of the fundamental asymmetry of linguistic systems. If there are phonemes, allophones and phonemic components, then there must also be morphemes, allomorphs and morphemic components. If there is a form and a substance of the expression, then there must also be a form and a substance of the content.