 The thought that our moral reasoning either requires or is benefited by a virtual quantitative crutch of this kind has a long pedigree. Can we really reason well morally in a way that boils down to assessing the weights of the competing considerations? Addressing this question will require an excursus on the nature of moral reasons. Philosophical support for this possibility involves an idea of practical commensurability. We need to distinguish, here, two kinds of practical commensurability or incommensurability, one defined in metaphysical terms and one in deliberative terms. Each of these forms might be stated evaluatively or deontically. The first, metaphysical sort of value incommensurability is defined directly in terms of what is the case. Thus, to state an evaluative version: two values are metaphysically incommensurable just in case neither is better than the other nor are they equally good (see Chang 1998). Now, the metaphysical incommensurability of values, or its absence, is only loosely linked to how it would be reasonable to deliberate. If all values or moral considerations are metaphysically (that is, in fact) commensurable, still it might well be the case that our access to the ultimate commensurating function is so limited that we would fare ill by proceeding in our deliberations to try to think about which outcomes are “better” or which considerations are “stronger.” We might have no clue about how to measure the relevant “strength.” Conversely, even if metaphysical value incommensurability is common, we might do well, deliberatively, to proceed as if this were not the case, just as we proceed in thermodynamics as if the gas laws obtained in their idealized form. Hence, in thinking about the deliberative implications of  incommensurable values,  we would do well to think in terms of a definition tailored to the deliberative context. Start with a local, pairwise form. We may say that two options, A and B, are deliberatively commensurable just in case there is some one dimension of value in terms of which, prior to – or logically independently of – choosing between them, it is possible adequately to represent the force of the considerations bearing on the choice. 