PIE was an inflected language, in which the grammatical relationships between words were signaled through inflectional morphemes (usually endings). The roots of PIE are basic morphemes carrying a lexical meaning. By addition of suffixes, they form stems, and by addition of desinences (usually endings), these form grammatically inflected words (nouns or verbs). PIE roots are understood to be predominantly monosyllabic with a basic shape CvC(C). This basic root shape is often altered by ablaut. Roots which appear to be vowel initial are believed by many scholars to have originally begun with a set of consonants, later lost in all but the Anatolian branch, called laryngeals (usually indicated *H, and often specified with a subscript number *h₁, *h₂, *h₃). Thus a verb form such as the one reflected in Latin agunt, Greek ἄγουσι (ágousi), Sanskrit ajanti would be reconstructed as *h₂eǵ-onti, with the element *h₂eǵ-constituting the root per se.

The roots of the reconstructed Proto-Indo-European language (PIE) are basic parts ofwords that carry a lexical meaning, so-called morphemes. PIE roots usually have verbalmeaning like "to eat" or "to run". Roots never occur alone in the language. Completeinflected words like verbs, nouns or adjectives are formed by adding further morphemes to a root. Typically, a root plus a suffix forms a stem, and adding an ending forms a word.[1]

For example, *bʰéreti[2] "he carries" can be split into the root *bʰer- "to carry", the suffix *-e- "present tense" and the ending *-ti "thirdperson singular".[3]

In its base form, a PIE root consists of a single vowel, preceded and followed by consonants. Except for a very few cases, the root is fully characterized by its consonants, while the vowel may alternate, a process called ablaut. Thus, the mentioned root *bʰer- can also appear as *bʰor-, with a long vowel as *bʰēr- or *bʰōr-, or even unsyllabic as *bʰr-, in different grammatical contexts.

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