Null morpheme

In morpheme-based morphology, a null morpheme is a morpheme that is realized by a phonologically null affix (an empty string of phonological segments). In simpler terms, a null morpheme is an "invisible" affix. It is also called a zero morpheme; the process of adding a null morpheme is called null affixation, null derivation or zero derivation. The concept was first used over two thousand years ago by 4th century Sanskrit grammarian from ancient India, Pāṇini, in his Sanskrit grammar. Some linguists object to the notion of a null morpheme, arguing that it sets up an unverifiable distinction between a "null" or "zero" element, and nothing at all.

The null morpheme is represented as either the figure zero (0) or the empty set symbol Ø.

The existence of a null morpheme in a word can also be theorized by contrast with other forms of the same word showing alternate morphemes. For example, the singular number of English nouns is shown by a null morpheme that contrasts with the plural morpheme -s.