Martin (1992: 194):
The distinction between condition and purpose has to do with modulation again. Purposives contain an additional modulation of inclination, associated with the Effect (the Effect is desired). This can be brought out by comparing hypotactic and paratactic realisations of the purposive relation; these proportionalities also reveal another peculiarity of purposive relations, namely that desire for Effect commences before the Cause — wanting to win, get there on time and give the opposition a chance are the motivation for, not the results of, training hard, driving fast and skating slowly in the examples below (with all other consequential relations the Cause is temporally anterior):
we trained hard so that we'd win :we wanted to win, and so we trained hard ::
we drove fast in order to get there on time :we were keen to get there on time and so we drove fast ::
we skated slowly to give them a chance :we were willing to give them a chance and so we skated slowly
This is the second of two critiques of this extract.
 Contrary to the claim, none of the paratactic clause complexes involves the logical relation of cause: purpose. In all three, the relation is cause: reason (see Halliday & Matthiessen 2004: 411). This can be demonstrated by substituting and therefore for and so:
we wanted to win, and therefore we trained hardThe proportionality is thus hypotactic purpose : paratactic reason.
we were keen to get there on time and therefore we drove fast
we were willing to give them a chance and therefore we skated slowly
The paratactic clauses, therefore, unlike the hypotactic clauses, do construe a cause^effect relation.
 In each of the three paratactic clause complexes (of cause: reason), 'desire' is a feature of the clause construing the cause. That is, the "desire for Effect" does not "commence before" the Cause.