Halliday & Matthiessen (1999: 94, 44):
Selections are bidirectional. We have already seen that functions associated with paradigmatic types constitute 'structural properties' by which these types are distinguished and that selections provide further information about these 'properties'.
Thus Figure 1-12 above illustrates how a figure of spearing is characterised by reference to the function of Means, which selects for the thing 'spear'. Conversely, semantic types which are selected are characterised by the functional environment within which they are selected. Thus the weapon 'spear' is characterised by its potential for serving as Means in a figure of spearing. Similarly, part of the meaning of a 'conscious being' is that it has the potential for serving in the Senser role of a figure of sensing.