Halliday & Matthiessen (1999: 549):
There are perhaps five basic types of indeterminacy in the ideation base: ambiguities, blends, overlaps, neutralisations, and complementarities — although it should be recognised from the start that these categories are also somewhat indeterminate in themselves. What follows is a brief characterisation of each in turn:
(1) ambiguities ('either a or x'): one form of wording construes two distinct meanings, each of which is exclusive of the other.(2) blends 'both b and y'): one form of wording construes two different meanings, both of which are blended into a single whole.(3) overlaps ('partly c, partly z'): two categories overlap so that certain members display some features of each.(4) neutralisations: in certain contexts the difference between two categories disappears.(5) complementarities: certain semantic features or domains are construed in two contradictory ways.