In one usage, a stem is a form to which affixes can be attached. Thus, in this usage, the Englishwordfriendships contains the stem friend, to which the derivational suffix-ship is attached to form a new stem friendship, to which the inflectional suffix-s is attached. In a variant of this usage, the root of the word is not counted as a stem. In a slightly different usage, which is adopted in the remainder of this article, a word has a single stem, namely the part of the word that is common to all its inflected variants. Thus, in this usage, all derivational affixes are part of the stem. For example, the stem of friendships is friendship, to which the inflectional suffix -s is attached. Stems may be a root, e.g. run, or they may be morphologically complex, as in compound words or words with derivational morphemes. Hence, the stem of the complex English nounphotographer is photo·graph·er, but not photo. For another example, the root of the English verb formdestabilized is stabil-, a form of stable that does not occur alone; the stem is de·stabil·ize, which includes the derivational affixes de- and -ize, but not the inflectional past tense suffix -d. That is, a stem is that part of a word that inflectional affixes attach to.
In languages with very little inflection, such as English and Chinese, the stem is usually not distinct from the "normal" form of the word. However, in other languages, stems may rarely or never occur on their own. For example, the English verb stem run is indistinguishable from its present tense form. However, the equivalent Spanish verb stem corr- never appears as such because it is cited with the infinitive inflection and always appears in actual speech as a non-finite or conjugated form. Such morphemes that cannot occur on their own in this way are usually referred to as bound morphemes. In computational linguistics, the term "stem" is used for the part of the word that never changes, even morphologically, when inflected, and a lemma is the base form of the word. For example, given the word "produced", its lemma is "produce", but the stem is "produc" because of the inflected form "producing".
A list of all the inflected forms of a stem is called its inflectional paradigm. The paradigm of the adjectivetall is given below, and the stem of this adjective is tall.
tall ; taller ; tallest
Some paradigms do not make use of the same stem throughout; this phenomenon is called suppletion. An example of a suppletive paradigm is the paradigm for the adjective good: its stem changes from good to the bound morphemebet-.
good ; better ; best
Oblique stem
Both in Latin and in Greek, the declension of some nouns uses a different stem in the oblique cases than in the nominative and vocative singular cases. Such words belong to, respectively, the so-called third declension of the Latin grammar and the so-called third declension of the Ancient Greek grammar. For example, the genitive singular is formed by adding -is or -ος to the oblique stem, and the genitive singular is conventionally listed in Greek and Latin dictionaries to illustrate the oblique.
