Truth-Conditional Meaning

Truth conditions are among the most foundational concepts in semantics. As Heim and Kratzer open their textbook, to know the meaning of a sentence is to know its truth conditions: hearing "There's a bag of potatoes in my pantry," one may not know whether it is true, but one does know what the world would have to be like for it to be true.

The key is that truth conditions describe the meaning of a whole sentence, not of an individual morpheme. A morpheme's meaning is its contribution to a context, but a sentence expresses a complete thought. Boy is not a complete thought; the boy ran is. In ordinary communication people do not parse out each morpheme separately but grasp complete thoughts and judge whether they correspond to what is known about the world.

Knowing the Word to Know the Truth

On hearing the bear escaped from the zoo, a hearer automatically asks whether that actually happened. Answering requires knowing the meanings of the words. If a red panda escaped, does the sentence hold? A red panda is not actually a bear, so the meaning of bear must be known to decide. If the bear walked out led by a trainer, does that count as escaping? Probably not, so the meaning of escape must be known as well. Determining whether the expressed thought is true depends on knowing what its words mean.

This is also what lets speakers understand novel sentences: successful communication requires that a hearer grasp what the world would have to be like for a statement to be true. There may be additional meaning present, such as implicatures, but at the most basic level a hearer must be able to pair the words with the appropriate state of the world.

Limits and Debates

Sentence meaning is not exhausted by truth conditions, and the notion is actively debated. Some researchers revise or discard truth conditions in favor of alternatives, and some point to utterances that seem to lack truth conditions altogether, such as expressive meanings like "Ouch, that hurt" or simply "Ouch," which are hard to call true or false. Various ways of describing such meanings exist. Even so, truth conditions remain an essential concept for doing semantics, and they connect closely to compositionality, since the truth conditions of a whole sentence are built from the meanings of its parts and the way they combine.