Reduplication is a morphological operation copying part or all of a root to express grammatical or semantic meaning: full reduplication (entire root repeated), partial reduplication (initial CV, final syllable, etc.), and templatic reduplication. Common meanings include plurality, aspect (habitual, iterative), diminution, and intensity.
From your study of morpheme types and morphological structure, you know that languages build complex words by combining morphemes — some free, some bound, some derivational, some inflectional. Reduplication is a morphological process that differs from affixation in a fundamental way: instead of adding an independent morpheme, the grammar copies phonological material from the root itself. The copied material is the morpheme. This makes reduplication one of the clearest demonstrations that morphology can operate on phonological form directly.
Full reduplication repeats the entire root: Tagalog *takbo* ("run") → *takbo-takbo* ("run around, run repeatedly"). The doubled form signals iterative or habitual meaning — the action occurs again and again. This pattern is strikingly cross-linguistic. Indonesian, Malay, many Bantu languages, and numerous others use full reduplication for plurality or repeated action. The consistency suggests that the meaning of "doing something again and again" maps naturally onto the form of "saying something again and again."
Partial reduplication copies only a portion of the root — typically the first syllable, the initial consonant-vowel sequence (CV), or the final syllable. In Tagalog again, *sulat* ("write") → *su-sulat* ("will write"), where the initial syllable reduplicates to mark future aspect. The reduplicant is not a fixed morpheme with its own phonological content: it is a template that gets filled in by copying. This is where templatic reduplication becomes the formal account: the morpheme specifies only a phonological shape (e.g., CV or CVC), and the actual sounds are supplied by copying from the base. The result is that the reduplicant sounds like the root — because it literally is part of the root.
The meanings expressed by reduplication cluster around a recognizable set of semantic and grammatical functions: plurality (especially of nouns referring to things in scattered or diffuse sets), iterativity or habituality of actions, diminutives (smaller, cuter, less intense), intensifiers (more, very), and attenuation (sort of, approximately). These meanings are not arbitrary — they reflect an iconic relationship between form and meaning. Repetition in form iconically represents repetition or diffuseness in meaning. This iconicity is rare in language (most morphological relationships are arbitrary), making reduplication a theoretically interesting case where form and meaning are systematically motivated.