Full Idea
It is clear that someone who knows under what conditions a sentence would be true understands that sentence, …and if someone does not know under what conditions it would be true then they do not understand it.
Gist of Idea
Knowing the potential truth conditions of a sentence is necessary and sufficient for understanding
Source
Donald Davidson (Truth Rehabilitated [1997], p.13)
Book Reference
Davidson,Donald: 'Truth, Language and History' [OUP 2005], p.13
A Reaction
I've always subscribed to this view. Langauge is meaningless if you can't relate it to reality, and I don't think there could be a language without an intuitive notion of truth.