Halliday & Matthiessen (1999: 522):
In its ideational metafunction, language construes human experience — the human capacity for experiencing — into a massive powerhouse of meaning. It does so by creating a multidimensional semantic space, highly elastic, in which each vector forms a line of tension (the vectors are what are represented in our system networks as “systems”). Movement within this space sets up complementarities of various kinds: alternative, sometimes contradictory, constructions of experience, indeterminacies, ambiguities and blends, so that a grammar, as a general theory of experience, is a bundle of uneasy compromises. No one dimension of experience is represented in an ideal form, because this would conflict destructively with all the others; instead, each dimension is fudged so that it can co-exist with those that intersect with it.