Halliday & Matthiessen (1999: 413):
We have already seen that the textual metafunction is a powerful part of the explanation of ideational metaphor: ideational meaning is reconstrued in such a way that it suits textual organisation when meanings are being distributed in text. This is an area where the evolved system of English and designed systems such as logics differ sharply: the latter are not designed to construe textual differences and instead place a high value on canonical forms.