Final answer:
The sounds [f] and [v] are contrastive in English and represent two different (a) phonemes. Phonemes are essential for differentiating words in a language, while allophones are variations of a phoneme that don't change word meaning. The English alphabet expresses these sounds with specific letters and sometimes alternate spellings.
Step-by-step explanation:
If [f] and [v] are contrastive in English, it means that they are two different phonemes in English. Phonemes are the smallest units of sound that can differentiate meaning between words. For instance, the word 'fine' contains the phoneme [f], while the word 'vine' contains the phoneme [v]. The distinction between the two sounds is critical because it changes the meaning of the word.
The term contrastive in phonology means that swapping one sound for the other creates a different word, which is exactly what happens with [f] and [v] in English. This contrast illustrates the significance of phonemes in a language's sound system. Allophones, on the other hand, are variations of a single phoneme that do not change the meaning of a word when they are used interchangeably.
As for the English alphabet, [f] is typically spelled <f>, but sometimes it can be spelled as <ff>, <ph>, or <gh>, while the sound [v] is spelled <v>—except in one word where it is spelled <f>.