Inflectional rules
Inflectional rules are used to generate the inflected forms out of the base form. They differ from inflectional paradigms in the sense that they are specific to particular words (i.e., they are used to generated only irregular forms),
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When to use inflectional rules
Inflectional rules should be used when the inflectional behaviour of a word is too specific (i.e., irregular).
When not to use inflectional rules
Inflectional rules should be avoided whenever there can be stated a regular pattern for inflecting words. In this case, the inflectional behaviour should be described by an inflectional paradigm.
Example
The plural of English nouns is considerably regular and can be treated, in most cases, by the following inflectional paradigms:
| Paradigm | Rule | Description | Example |
| 1 | PLR:=0>"s"; | Add "s" to the end of the word | boy > boys |
| 2 | PLR:="y">"ies"; | Replace "y" by "ies" at the end of the word | city > cities |
| 3 | PLR:=0>"es"; | Add "es" to the end of the word | kiss > kisses |
| 4 | PLR:="f">"ves"; | Replace "f" by "ves" at the end of the word | woolf > woolves |
However, there are several special cases that, being very limited, should be treated by inflectional rules instead of inflectional paradigms:
| Rule | Description | Case |
| PLR:="men"; | Replace the whole word by "men" | man > men |
| PLR:="mice"; | Replace the whole word by "mice" | mouse > mice |
| PLR:="feet"; | Replace the whole word by "feet" | foot > feet |
| PLR:="children"; | Replace the whole word by "children" | child > children |
| ... | ... | ... |
The difference between inflectional paradigms and inflectional rules is mainly a question of frequency. If a rule is applicable to several different words, it should be defined as a general inflectional paradigm; if it is applicable to a single word or to a very limited number of cases, it should be defined as an inflectional rule inside the very entry.
Syntax
Inflectional rules should comply with the M-rule formalism for writing morphological rules in the UNL framework.
Observation
Inflectional rules can be combined with inflectional paradigms in order to describe localized irregular behaviour.
