Modal adjectives are adjectives, such as likely, probable and necessary, that express modality, i.e., possibility, necessity, or contingency.[1][2]
In English
Modal adjectives can express modality over a situation or a participant in that situation. For situations, the usual syntactic construction includes an extraposed subject,[3] such as the underlined elements in the following examples with the modal adjective in bold. Here the modal adjective is analyzed semantically as a sentential modal operator.[3]
- It's possible that some of them are broken.
- It's likely that they will come.
- It is necessary (for us) to make a choice.
For participants, however, the usual syntactic construction has the adjective phrase in attributive modifier function,[3] as in the following examples, where the modal adjective is again in bold and this time the participant in underlined.
- We've found a potential replacement.
- They need to file the necessary papers.
- We took the obligatory photo.
Other constructions are also possible. For example, contingency may be expressed as We've made an offer contingent on the sale of our house, which can be paraphrased as Our offer stands if and only if we sell our house.
In Japanese
In Japanese, possibility is often expressed with the adjectives 可能 (kanou 'possible') and 不可能 (fukanou 'impossible'), as in 目標を実現することは不可能です (Mokuhyou o jitsugen suru koto wa fukanoudesu 'It's impossible to realize that goal'). Impossibility can also be expressed with the modal adjective 無理 (muri 'impossible') as in, 円を7で等分することは無理です (en o nana de toubun suru koto ha muri desu 'a circle cannot be divided into seven equal parts').
The modern Japanese particle べき (beki 'should') derives from the traditional modal adjective べし (beshi) but no longer inflects.[4]