The complications possible in the systematisation of impulses might be illustrated indefinitely. The plasticity of special appetencies and activities varies enormously. Some impulses can be diverted more easily than others. Sex has a wider range of satisfactions than hunger, for example; some are weaker than others; some (not the same necessarily) can be suppressed in the long run with less difficulty. Some can be modified; some obey the ‘all or none’ rule—they must either be satisfied specifically or completely inhibited—well-established habits may have this peculiarity. In judging the importance of any impulse all these considerations must be taken into account. The affiliations of impulses, at present often inexplicable, need especially to be considered. Within the whole partially systematised organisation, numerous sub-systems can be found, and what would be expected to be quite trivial impulses are often discovered to be important, because they belong to powerful groups. Thus there are reasonable persons who, without a high polish on their shoes, are almost incapacitated. The importance of an impulse, it will be seen, can be defined for our purposes as _the extent of the disturbance of other impulses in the individual’s activities which the thwarting of the impulse involves_. A vague definition, it is true, but therefore suitable to our at present incomplete and hazy knowledge of how impulses are related. It will be observed that no special ethical idea is introduced. We can now take our next step forward and inquire into the relative merits of different systematisations.