The Russian consonant [v] has played a key role in discussions about abstractness in phonology, about the manner in which long-distance spreading occurs, and about the the larger organization of phonology. This is largely because of the odd behavior of [v] with respect to final devoicing and voicing assimilation in Russian. Like an obstruent, it devoices word-finally and undergoes voicing assimilation. But like a sonorant, it does not trigger voicing assimilation.
Why is Russian [v] special in this way? The best-known answer to this question posits that [v] is underlyingly /w/ and therefore behaves as a sonorant with respect to voicing assimilation. Since those accounts posit that [v] is an obstruent on the surface, this is a classic example of derivational opacity, and one that has not been adequately addressed in the framework of Optimality Theory. In spite of the great elegance of the derivational account, I will argue for a different view: Russian [v] is in fact more sonorous at the surface than any other Russian obstruent—though it is not a glide—and all of its unusual properties can be plausibly explained by considering in greater detail the phonetic properties of such a sound. Independent evidence for these claims comes from phonetic studies of [v], and from typological considerations. It follows that no serial ordering of rules or processes is required in order to explain the behavior of this sound; there is no need to call on any intermediate representation at which [v] is [w] or anything else. The account therefore bears on the general question of whether this sort of derivationality and abstractness are necessary to phonology.