Halliday & Matthiessen (1999: 249):
… we identified individual types of grammatical metaphor, such as "process => thing". For analytic purposes we treated these as isolates having just the two values "congruent/ metaphorical". We now need to consider two respects in which this is an idealised, oversimplified account of what actually happens. We need to add a dimension of complexity on both syntagmatic and paradigmatic axes.Syntagmatically, instances of grammatical metaphor typically occur not in isolation but in organic clusters or "syndromes". Paradigmatically, there will typically be other wordings intermediate between an instance of grammatical metaphor and its "most congruent" agnate variant.