Evidence presented in the previous chapter suggests that flotation in liquids is associated with a partially theoretical structure. Variables are generated by mechanisms to be sure, but at the same time many variables lie beyond the scope of mechanisms. Seeking to interpret this, the previous chapter called upon the lack of orthodoxy displayed by many children in their choice of mechanisms. This, it was proposed, should lead to waywardness over variables, negative feedback on usage, unprincipled substitution of new variables, and gradual severance from mechanisms. The scenario was contrasted with the situation relating to the transfer of heat, where the more ‘respectable’ mechanisms should (and seemingly do) result in a tighter theoretical structure. Yet while the contrasts were spelled out, the previous chapter recognised the core similarity between flotation in liquids and heat transfer which stemmed from their mutual reliance upon theory. This, it was argued, not only brings the two topic areas together but also sets them apart from propelled motion, as discussed in part III. Since flotation in liquids is, from the received perspective, a specific instance of propelled motion, this is not merely ironic; it suggests also that the segmentations which are fundamental within everyday physics are very different from those which apply within orthodox science.