The Distinction Between ‘Contrastive In Tense’ And ‘Contrastive In Polarity’

Halliday & Matthiessen (2014: 411):

The distinction between ‘contrastive in tense’ and ‘contrastive in polarity’ is realised only if at least one secondary tense is chosen; it is however regarded as systemic in all instances, with ambiguity arising where there is no secondary tense.

Verbal Group Systems By Metafunction

Halliday & Matthiessen (2014: 411):

The systems of the verbal group derive from different metafunctions:

(i) Textual: voice, contrast and ellipsis; 

(ii) Interpersonal: polarity, finiteness and modality; 

(iii) Experiential: aspect and event type; 

(iv) Logical: secondary tense.