An opposition between two linguistic elements is neutralized in a particular context iff either or both of the elements are excluded from that context.
In the context of neutralization, one of the following alternatives happens:
- only one member of the opposition appears (in which case the opposition is neutralized in favor of that element)
- the members of the opposition appear as variants of each other
- a third element appears (which may or may not be similar to the elements which are expected).
A phonological opposition may be neutralized at the level of phonotaxis. As an example of alternative #1, English /p/ and /b/ contrast in most positions, but the opposition is neutralized - in favor of /p/ - after syllable-initial /s/. Otherwise, it may be neutralized by a phonological rule. For instance, German voiced and voiceless obstruents contrast in the syllable onset. If, however, a voiced obstruent ends up in the coda, the opposition is neutralized in favor of its voiceless counterpart.
The Spanish opposition between [r] and [ɾ] is neutralized in the coda. The European standard here applies alternative #2 of the neutralization: in this position, [ɾ] is the default, [r] occurs under emphasis. Some American dialects apply alternative #3: some use [r̝] or [z̝] (as does Brazilian Portuguese in the analogous case), others use [l].