  The big question facing pluralism is whether rational choices can be made between irreducibly plural values. Irreducible plurality appears to imply incommensurability—that is to say, that there is no common measure which can be used to compare two different values. (See the entry on  incommensurable values.)  Value incommensurability seems worrying: if values are incommensurable, then either we are forced into an ad hoc ranking, or we cannot rank the values at all.  Neither of these are very appealing options. 