Full Idea
We have the idea of belief from its role in the interpretation of language; as a private attitude it is not intelligible except in relation to public language. So a creature must be a member of a speech community to have the concept of belief.
Gist of Idea
The concept of belief can only derive from relationship to a speech community
Source
Donald Davidson (Thought and Talk [1975], p.22)
Book Reference
'Mind and Language', ed/tr. Guttenplan,Samuel [OUP 1977], p.22
A Reaction
This shows how Wittgenstein's Private Language Argument (e.g. Idea 4152) hovers behind Davidson's philosophy. The idea is quite persuasive. A solitary creature just follows its mental states. The question of whether it believes them is a meta-thought.
Related Idea
Idea 4152 Getting from perceptions to words cannot be a private matter; the rules need an institution of use [Wittgenstein]