Concept
In ethics, two values (or norms, reasons, or goods) are incommensurable (or incommensurate, or incomparable) when they do not share a common standard of measurement or cannot be compared to each other in a certain way. There is a cluster of related ideas, and many philosophers use the terms differently. On one common usage: Two values (for example, freedom and security) are incommensurable when they cannot be 'traded off' against each other: for example, if there is no set amount of freedom that would compensate for a certain loss of security, or vice versa. Two options or choices are incommensurate or incomparable if and only if: it is not true that one is better, that the other is better, or that they are exactly equally good. This page is concerned almost entirely with the second phenomenon. For clarity, the term 'incomparable' is used. In terminology due to Ruth Chang, the three trichotomous comparisons are betterness, worseness, and equal goodness. For example, one artist, drawing, or cup of coffee might be better or worse than another, or precisely equally as good as it. When two items are incomparable, none of the trichotomous comparisons holds between them (or at least it seems that way). The clearest way of arguing that two options are incomparable is a small-improvement argument. The purpose of such examples is to show that none of the trichotomous comparisons apply. Here is an example. Suppose that (for you, taking everything into account) a certain job as a professor and a certain job as a banker are such that neither seems better than the other. The professor job offers more freedom and security, and the banking job offers more money and excitement. But we might say that though they are good in different ways, they are just too different to be compared with one of the trichotomous comparisons. Let's suppose that this means that the banking job is not better, and the professor job is not better. This seems to rule out two of the three trichotomous comparisons.