Inflection morphology in a formal grammar

Inflectional morphology can be fit together with syntax in a formal grammar.


Grammar builds a sentence in two phases: first syntax, then inflectional morphology. In the syntactic phase, the phonological material of inflectional affixes is not inserted form the lexicon. Instead, inflectional morphology is represented in trees produced by the base solely by inflectional features on preterminal nodes. For a sentence like The boys cried, the base would produce a tree that looks like this (using phonetic transcription to represent actual pronunciation more accurately):

(11)   output of the base component for The boys cried.


the [+plural] on the N represents the plurality of boys and the [+past] on the verb represents the past tense of cried. The only phonological material at the terminal nodes belongs to the stems, exactly  as they are listed in the lexicon. A tree structure like (11), which is produced entirely by the base component, is called its DEEP STRUCTURE.

       This, of course, is incomplete. Somehow, the inflectional features need to be ‘spelled out’ by adding phonological material to the stems, such as /z/ and /d/.

(12)     Structure of The boys cried after spelling out inflectional affixes


this completes the process of generating the sentence. A tree structure like (12), which matches the actual sentences we are trying to produce, is called its SURFACE STRUCTURE.

Inflectional spellout rules

       To get from (11) to (12), we need one rule that adds –z to the end of any noun that is [+plural] and another that adds –d to the end of any verb that is [+past]. We call these rules INFLECTIONAL SPELLOUT RULES and write them as follows:

(13)     Inflectional spellout rules for noun plurals



                    [X]     à       [Xz]

(14)     Inflectional spellout rules for past tense on verbs



                    [X]     à       [Xd]

       Other features are more limited in their distribution. For example, [+plural] can only be allowed to appear on certain nouns. Other nouns, like software do not have plural forms (i.e., *softwares is not a grammatical English word). This latter group is called mass nouns. This means, before we can talk about plural forms of nouns, we must first divide the class of nouns into two subcategories in the lexicon, using the features [+count] and [-count].

(17)     N [+count]                                N [-count]

          sændwIt∫      sandwich                 sænd            sand

          kƏm`pju:tƏr  computer                softweƏ       software

when  a noun is inserted in a tree, we assume it carries with it all the features that it has associated with it in the lexicon (although we don’t usually write all of them). So every N node in every tree ends up with a feature for [count].

(18)     Partial trees, just after lexican insertion


then, we need feature assignment rules to add the feature [±plural]. But, this must be done selectively; mass ([-count]) nouns must always be [-plural], while count ([+count]) nouns can be either [+plural] or [-plural].

(19)      Feature assignment rules for English nouns

          N[-count]  à [-plural]

          N[+count] à [±plural]

When the rules are applied to the partial trees in (18), the choices in them allow any of the following results:

(20)      Completed deep structure trees, after all feature assignment rules have applied.

To summarize, we can add some detail to our diagram of  a formal grammar.

Irregular  inflectional in formal Grammars

       In every language, there are words that are INFLECTED IRREGULARLY, that is, which have some forms that do not follow the regular inflectional rules. These irregular, or SUPPLETIVE, forms must be listed in the lexicon, since they are not predictable by rule and must be learned individually. For example, the lexical entry of go might look like this:


QP      à       (DegP) Q

          DegP   à       . . .  Deg

          N[-count]      à       [-plural]

          N[+count]     à       [±plural]

  1. Lexicon (sample lexical entries)