Sub Specie Boni, Sub Ratione Boni: Imagination and Estimation in Aquinas's Guise of the Good

According to the thesis sometimes known as “the guise of the good”, we can only want or desire something (or intentionally do something) if it appears good to us in some respect. Typically, when introducing this thesis, one finds contemporary authors using the Latin phrase sub specie boni. In medieval Latin formulations, however, the standard formula is that whatever we will, we will sub ratione boni, or that we can only will something sub ratione boni, i.e. under the ratio (aspect) of good/goodness. Much more rarely does one find the expression sub specie boni, i.e. under the appearance or semblance of good/goodness. This seems especially true in Thomas Aquinas (1225-1274). First, I present textual evidence for this terminological difference in Aquinas, and show that sub specie boni occurs almost exclusively in contexts where the agent wants something on the basis of, mistakenly, taking something bad to be good. But why reserve sub specie boni for these cases? In the second part of the article, I compare the role played by the cognitive powers of imagination and estimation in the evaluations which are proposed to the will, concluding that not imagination, but estimation is, at least in part, the key to Aquinas’s view of the will. I also highlight differences between the evaluations of estimation and those of conscience. Once we bring out these contrasts, sub specie boni turns out to be an expression with its own significance, and not just a rhetorical variant of sub ratione boni.