A TMA system may be compared to a cake, a cake that it is always the same size, for TMA systems, whether simple or complex, all have to cover the same sentence area: every verb has to have some tense, mood, aspect, or combination of these applied to it, for there are […] no such things as “TMA-neutral” sentences. But a cake may be split up into five, or eight, or ten slices, just as a TMA system can divide its semantic area among five, or eight, or ten TMA markers and/or combinations of markers. If a cake is divided into five slices, there is no way in which each of the slices in Cake A can contain exactly the same amount of material as each of the slices in Cake B. In other words, how much, and exactly what, is contained in each slice will be largely determined by the number of slices. This is exactly the state of affairs in TMA systems throughout language; what each marker of modality , tense, or aspect means will be largely determined by how many markers of these things there are in the system and by what each of the others mean.
- Bickerton (1981), a pag.90