'enable' and ‘understand’ are lexical items realised as verbs…
It is very common to confuse lexical items with grammatical process types, which is why I am posting this reply to the list
 In SFL, lexical items are not realised by verbs — a lexical item is not more symbolically abstract than a verb.
A lexical item realises a composite of lexical features, whereas verb is a grammatical class at the rank of word. The two are therefore related in terms of delicacy, and the lexical item is less symbolically abstract.
Halliday & Matthiessen (1999: 568):
The folk notion of the “word” is really a conflation of two different abstractions, one lexical [lexical item] and one grammatical [word rank].
 The common error is to assign verbs to process types, not 'to confuse lexical items with grammatical process types'.