Halliday & Matthiessen (1999: 561-2):
It seems likely that all these different kinds of indeterminacy are what make it possible for the grammar to offer a plausible construal of experience — one that is rich enough, yet fluid enough, for human beings to live with. We should stress once again that the examples cited here are features of the ideation base of one particular language, namely English. No other language will be identical. Indeed the distribution of indeterminacies is likely to be precisely one of the features in which languages differ most, and even perhaps varieties within one and the same language. But every language depends on indeterminacy as a resource for meaning — even if our grammatics is not yet very clever at teasing it out.