Halliday & Matthiessen (1999: 223-4):
Sequences, figures and elements, and their subclasses, constitute different environments within the ideation base. If we construe some phenomenon of experience as a sequence of qualification, we give it a location in the overall ideational system that is quite distinct from the location it would be assigned if it was construed as a figure of circumstantial cause. These two types are thus not particularly close agnates in the system, However, the fractal types constitute an additional order of agnation that is projected onto the ideational system as a whole. We can refer to this as fractal agnation. Because of this, a qualifying sequence and a figure of circumstantial being, such as cause, are agnate: they are both manifestations of the fractal type of enhancement For example, the sequence ebola broke out so 52 people died is agnate with the figure the outbreak of ebola caused 52 deaths even though they are quite far apart in their semantic structure.