Some New Mechanists have proposed that claims of compositional relations are justified by combining
the results of top-down and bottom-up interlevel interventions. But what do scientists do
when they can perform, say, a cellular intervention, but not a subcellular detection? In such cases,
paired interlevel interventions are unavailable. We propose that scientists use abduction and we
illustrate its use through a case study of the ionic theory of resting and action potentials.