The morphological type of a language refers to the way morphemes combine into words.
1. Isolating (or analytic) languages have words that consist of one morpheme each. There probably is no ideal isolating language, but Chinese and Vietnamese come close. English is sometimes cited as an isolating language as well, even though it is not purely isolating, but weakly fusional.
2. Agglutinating languages have words that may consist of more than one morpheme; the morpheme boundaries are clear and the word can be easily broken up into morphemes. Each of the inflectional morphemes fulfils a single grammatical function. An example is Turkish:
(1a) ev 'house'
(1b) evde 'in the house'
(1c) evler 'houses'
(1d) evlerde 'in the houses'
The last form can be easily broken up into three morphemes: ev is the word stem (the same in all four forms), -ler the plural marker (the same as in (1c), and -de the locative case marker (the same as in(1b)).
3. Fusional languages have words that may consist of more than one morpheme; unlike agglutinating languages, the morpheme boundaries are blurred, and morphemes may express several grammatical categories in one unsegmentable unit. Most Indo-European languages are of this type. An example is Latin:
(2a) homo 'man' (nom. sg.)
(2b) homini 'man' (dat. sg.)
(2c) homines 'men' (nom. pl.)
(2d) hominibus 'men' (dat. pl.)
The stem form varies between homo in (2a) and homin- in the other forms; the form (2d) shows the dative plural ending -ibus which cannot be broken up into a dative and a plural morpheme (as comparison with (2b) and (2c) shows).
These three types are rarely met in pure form, but form a continuum in which each language finds its place. Agglutinating and fusional languages are often grouped together as synthetic languages. The term inflecting is often used for fusional, but sometimes also for synthetic languages in general. It is thus ambiguous and best avoided.
Two further common terms for morphological types are:
4. Polysynthetic languages are languages that are highly synthetic, with very complex words that can function as whole sentences, combining subject, object and verb in one word. Polysynthetic languages may be agglutinating or fusional.
5. Oligosynthetic languages are not really a morphological type, and they apparently do not occur among natural languages. An oligosynthetic language has only a limited set (a few dozen to a few hundred) of basic morphemes from which all words are built up.