Every spoken language contains a small number of basic sound units, or phonemes. Among the phonemes of English are /k/, /æ/ and /t/. If we produce these phonemes in the order /kæt /, we get the word cat. But the order /tæk/ gives us tack, while /ækt/ yields act, /æt/ gives at, and /tækt/ gives tact or tacked (which are pronounced identically, in spite of their different structures).