The two most important contributions of Trubetzkoy’s last volume are his detailed […] discussion of neutralization and junctures. Both of these are fairly new terms in linguistics, representing procedures of analysis which have only recently become explicit. Two phonemes may be contrasted in some positions but not in others, if in these other positions only one of them can occur. For example, English [b] and [p] are not contrasted after [s], because only one of them can occur after [s]. Neutralization (Aufhebung) is the term for such lack of contrast in specific positions. It is a relation analogous to positional variants and is central in the description of a phonemic distribution.
- Harris (1941), a pag.348

[…] most cases of ‘neutralization’ involve not merely two phonemes that directly neutralize each other. Usually several phonemes occur in a given position while several others do not, and ‘neutralization’ may be said to exist between the two whole classes of phonemes; thus after word-initial /s/ we find /p, t, k, f, l, w, y, m, n/ and the vowels, but not /b, d, g, v, θ, ð, š, ž, s, z, r, ŋ, h/. To select /p/ and /b/ out of the two lists and assign them to a separate archiphoneme P implies some further and hitherto unformulated method of phonemic classification on phonetic grounds. And what shall we do with /θ/ or /š/ or /z/?
- Harris (1941), a pag.183