Misconstruing Negative Vs Positive Purpose

Martin (1992: 195-6):

Contingent relations make a distinction between conjunctions incorporating negative polarity (unless and lest) and those which don't.  The relevant proportionalities and relevant paradigm are as follows:

UNLESS : IF…NOT ::

LEST : SO THAT…WILL + NOT 

unless Ben plays you'll lose :

if Ben doesn't play you'll lose :: 

Ben'll play lest you lose :

Ben will play so that you won't lose

But the opposition between "positive" and "negative" values has a different meaning in the context of conditional relations from that in purposives. … With purposives, the opposition is between [desire] and [fear].  So that encodes a inclination to achieve the Effect, lest an inclination to avoid it:

DESIRE

[4:62]  He went that way

            so that he'd get there by six.

FEAR

[4:63]  He went that way

            lest he lose his way. (less archaically: for fear of losing his way.)

Blogger Comments:

[1] Because it is a category error to construe the logical meaning of purpose, because intention P, so action Q as 'desire (for Effect)', it is also a category error to construe the negative agnate as 'fear (of Effect)'.

[2] This confuses the logical and interpersonal metafunctions.  Just as the logical relation of purpose is distinct from the interpersonal feature inclination, so too is the negative agnate.

[3] Compounding the previous confusion, the terms 'achieve' and 'avoid' distinguish the positive and negative poles of inclination in terms of conation, instead of dis/inclination.

[4] The logical meaning of purpose does not include the relation of cause and effect.  In the 'purpose' nexus she cast a spell to ward off evil spirits, warding off evil spirits is the purpose, but not the effect of casting a spell.  Cause and effect appear in complexes where clauses are related by cause: reason (or cause: result).