The Ordering Of Finite And Predicator

Halliday & Matthiessen (2014: 152):

… a finite verbal group serves as both Finite and Predicator … . When the Finite and the Predicator are not fused, the Predicator follows the Finite, but certain other elements may come between them, making the verbal group discontinuous: the Subject in ‘interrogative’ clauses where the Finite precedes the Subject (as in can <you> tell) and Adjuncts (as in had <originally> planned to present.