An important concept is that of the minimal-pair.
Minimal pair: a minimal pair is a set of precisely two words (both from the same language) that differ by only a single phoneme; the two words must be recognisable by speakers as being two different words
Examples of minimal pairs are:
pin vs. bin (words differ in the phonemes /p/ vs. /b/)
pit vs. sit (words differ in the phonemes /p/ vs. /s/)
pit vs. put (words differ in the phonemes /i/ vs. /u/)
pun vs. fun (words differ in the phonemes /p/ vs. /f/)
In each of the above examples, the two words fulfill a crucial condition of minimal pairs: They differ in precisely one sound (phoneme).
The following examples, by contrast, are not minimal pairs:
pin – pin (because the words do not differ in any sound, they are identical)
pin – ring (because the words differ in more than just one sound)
