In English grammar, a base is the form of a word to which prefixes and suffixes can be added to create new words. For example, instruct is the base for forming instruction, instructor, and reinstruct. Also called a root or stem.
Put another way, base forms are words that are not derived from or made up of other words. According to Ingo Plag, "The term 'root' is used when we want to explicitly refer to the indivisible central part of a complex word. In all other cases, where the status of a form as indivisible or not is not an issue, we can just speak of bases (or, if the base is a word, base words)" (Word-Formation in English, 2003).
Examples and Observations
"In most situations, the user of English has no problem at all recognizing prefixes, bases, and suffixes. For instance, in the sentence, 'They repainted the old car,' the complex word repainted obviously has three elements--a prefix, a base, and a suffix: re + paint + ed. The base paint is the word's semantic core, the starting place for describing what the word is being used to mean in a given utterance. The prefix and suffix add semantic content to that core, the prefix re adding the content 'again,' and the suffix ed adding 'in the past.'" (D. W. Cummings, American English Spelling. JHU Press, 1988)
Base Forms and Word Roots
"The term base refers to any part of a word seen as a unit to which an operation can be applied, as when one adds an affix to a root or stem. For example, in unhappy the base form is happy; if -ness is then added to unhappy, the whole of this item would be considered the base to which the new affix is attached. Some analysts, however, restrict the term 'base' to be equivalent to 'root,' the part of a word remaining when all affixes have been removed. In such an approach, happy would be the base form (the highest common factor) of all its derivations-
happiness, unhappy, unhappiness, etc. This meaning leads to a special use in prosodic morphology to define the portion of the output in correspondence with another portion of the form, especially the reduplicant." (David Crystal, Dictionary of Linguistics and Phonetics, 6th ed. Blackwell, 2008)
"For adjectives, e.g. bad, the base form is the so-called 'absolute' form (as against the comparative form worse, or the superlative form worst). For other word classes, e.g. adverb or preposition, where there are no grammatical variants, there is only one form that can be the headword.
"These base forms of words, the headwords of dictionary entries, may be termed the citation forms of lexemes. When we want to talk about the lexeme sing, then the form that we cite (i.e. 'quote') is the base form--as I have just done--and that is taken to include all the grammatical variants (sings, singing, sang, sung)." (Howard Jackson, Words and Their Meaning. Routledge, 2013)
Bases in Complex Words
"Another classic problem of morphology is the case of a complex word with a recognizable suffix or prefix, attached to a base that is not an existing word of the language. For example, among the -able words are words such as malleable and feasible. In both cases the suffix -able (spelled -ible in the second case because of a different historical origin for the suffix) has the regular meaning 'be able,' and in both cases the -ity form is possible (mealleability and feasibility). We have no reason to suspect that able/ible here is not the real suffix -able. Yet if it is, then malleable must be broken down as malle + able and feasible as feas + ible; but there are no existing words (free morphemes) in English such as malle or feas, or even malley or fease. We thus have to allow for the existence of a complex word whose base exists only in that complex word… " (A. Akmajian, R. A. Demers, A. K. Farmer, R. M. Harnish, Linguistics: An Introduction to Language and Communication. MIT, 2001)