Why your brain treats 'cats' and 'dogs' as the same underlying sound

Cultures · Published 30 September 2026 Swipe more like this →

In short: You might think the plural 's' in cats and dogs sounds different, but your mind processes them as the same underlying unit. Morphophonology reveals how our brains bridge the gap between abstract word meanings and the messy, shifting sounds we actually produce when we speak.

Morphophonology, also known as morphophonemics, is the linguistic study of how sound changes occur when meaningful units, or morphemes, combine to form words. While a phoneme is the smallest unit of sound, a morphophoneme is a theoretical underlying representation—a stable mental anchor for a morpheme that persists even when its surface pronunciation shifts due to its environment.

Consider the English plural suffix. While written as '-s' or '-es', it is pronounced as [s], [z], or [ɪz] depending on the preceding sound. Linguists analyze these variations as a single underlying morphophoneme, ⫽z⫽, which is transformed into different surface sounds by specific rules. This process is not limited to simple suffixes; it explains complex phenomena like vowel harmony in Turkic languages, consonant gradation in Uralic languages, and the ablaut patterns seen in Germanic verbs like sing, sang, and sung.

Historically, linguists once split the analysis into two distinct stages: a morphophonological phase to derive phonemes from morphophonemes, followed by a purely phonological phase to produce actual speech sounds. Since the 1960s, particularly following the work of Noam Chomsky and Morris Halle in The Sound Pattern of English, many have moved toward a unified system. This approach uses formal rules—such as feeding, bleeding, counterfeeding, and counterbleeding—to predict how underlying forms evolve into the sounds we hear.

This framework also explains why our writing systems often prioritize morphophonological structure over pure phonetics. We write the plural as '-s' in both cats and dogs because it reflects the underlying morpheme rather than the phonetic reality. Similarly, many English spellings preserve etymological links, such as the relationship between sign and signature, helping us navigate the complex, dynamic interactions between word formation and sound patterns.

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