Inflectional fusion refers to the classification of grammatical formants or markers based on the manner in which they attach to “hosts” or roots. Isolating morphemes function as standalone words (also termed externally analytic morphology). Phonologically bound, concatenative formants attach to hosts to form a phonological word, creating morphological alternation in a process known as (partial) fusion. Clitics constitute a subclass of concatenative formatives. Although clitics are syntactically classified as words[1], they fulfill the criteria of concatenative morphemes. Concatenative formatives fall into two types: linear and non-linear. Linear formatives can easily undergo morphological segmentation, despite alternation, while non-linear formatives modify the roots themselves, triggering internal flexion or syntheticism.[2] Non-linear formatives can be further classified into two strategies: ablaut, or the alternation of vowels or consonants, which is marked by the inseparability of the stem and formant, neither of which appear in their base form, and tone, in which the pitch of vowels is used to express grammatical content.

For the purpose of this parameter, languages are classified according to the strategies they employ. This can be determined by examining the marking of case and sometimes number.

Types:

Isol: The marking of case (and number) is exclusively isolating.

ConcLin: The marking of case (and number) is exclusively concatenative, primarily with linear strategies.

ConcAbl: The marking of case (and number) is exclusively concatenative, primarily with ablaut strategies.

Ton: The marking of case (and number) is exclusively tonal.

When a language displays more than one type, multiple values can be listed. If one type is dominant, a slash (/) can separate the two values, with the dominant value appearing first; if neither is dominant, they are listed with an ampersand (&) separating the two.

[1] Syntactic relations are characterized by (1) the ability of their components to appear independently, (2) belonging to syntactically distinct nodes, (3) the lack of a fixed order among the given components, (4) the ability of these components to appear independently in order to mark focus, and (4) the presence of agreement among these components. If these criteria fail to be met, the presence of either independent stress or prosodic independence (consisting of more than one mora) may also indicate that a word is syntactically independent.

[2] Linear concatenation may be divided into subtypes: agglutinative, if the morphemes are analytic (also known as monoexponential: one function expressed by a single morpheme); flectional, if the morphemes are synthetic (polyexponential: multiple functions expressed by a single morpheme, such as case and number). For more information on these subtypes, see the parameter Case exponence.