  But one might still worry that moral judgments that rested on probable matters of fact were less secure than those found to be in accordance with eternal fitnesses, even with the aforementioned advantages. Seven years later, Butler offered a methodological argument in the “Introduction” to the Analogy that might respond to this objection if applied to morals (although Butler framed the point more generally). Although deductive arguments like those championed by Clarke were secure when considered abstractly, they were open to doubt when applied to matters of fact about actions or characters. This was because one needed a hypothesis of how to apply the abstract demonstrative truths to observed facts (“Introduction” §7) — how to fit the fitnesses to actions so to speak — and this hypothesis itself was not deductively secure. Butler offered the analogy of Cartesian physiology. Cartesian physiology applies Cartesian geometry to living bodies. But one needs a probable hypothesis to move from the abstract truths of Cartesian geometry to actual bodies and diseases. For example, “this spleen is roughly an oval and the way it interacts with the liver roughly results in this sort of mechanism”. The mechanism itself as represented abstractly is a certain geometrical relationship. But in order to apply the mechanism to blood and guts, one needs to have a probable, i.e. not certain, hypothesis about how the ideal mechanism fits with the facts on the ground — that this arrangement of blood and guts is best captured by this mechanism not that one. A similar problem arises when applying eternal and abstract relations to particular moral circumstances and actions. The need for a hypothesis as to how the relations might fit actual actions rendered the evaluation of the action merely probable even though the rightness and wrongness to which the action was to conform — the eternal fitness — was known certainly.