(1) I want to buy him a present
want | to buy: a ' b
(2) I want to try to convince him to come
want | to try | to convince: a ' b + c
(i.e. projection and extension)
(1) conjunctions form a word class within the primary word class of adverbials [Halliday & Matthiessen 2004: 358];(2) Premodifiers in adverbial groups are grammatical items — there is no lexical premodification in the adverbial group [op cit: 356];(3) items serving as Premodifiers in adverbial groups are adverbs of polarity, comparison or intensification [ibid];(4) all the examples given of Premodifiers in conjunction groups are grammatical items (even, just, not, only), not lexical items [op cit: 358].