Subjacency

In linguistics, specifically within transformational grammar, subjacency is a constraint that limits the movement of constituents (phrases or words) within a sentence. It posits that movement cannot occur across more than one bounding node. Bounding nodes are designated syntactic categories (like noun phrases (NP) or sentences (S)) that act as barriers. subjacency aims to explain why certain grammatical transformations, such as wh-movement (moving a 'wh-' word like 'who' or 'what'), are permissible in some cases but not in others, based on the hierarchical structure of the sentence. It’s a core principle influencing sentence well-formedness and the recoverability of information for parsing. The concept significantly impacts how linguists model and analyze sentence structure.

Subjacency meaning with examples

• Consider the question, 'What did John say Mary bought?' subjacency permits the movement of 'what' from the object position within the embedded clause ('Mary bought what'). The 'wh-' word can move over the verb 'say' and the matrix sentence boundary because the single bounding node (S') is not violated. This illustrates a grammatical application allowed within this concept. However, if a sentence breaks this single jump, it can be grammatically unaccepted.
• In contrast, consider a complex sentence: 'Who believes that the claim that John saw Mary is true?' The movement of 'who' out of the embedded clause faces more than one bounding node. If subjacency violations are enforced and the movement is required across multiple boundaries, the extraction may result in ungrammaticality. Thus, it is prohibited by the subjacency principle because a violation of more than one bounding node occurs making it unacceptable.
• The sentence 'What do you wonder who bought?' is often considered acceptable because the 'what' moves out of a single clause, not multiple bounding nodes. This makes the sentence structure clear in its intention. Even if it moves around other sentence components it must remain with the same one. Other examples of questions can be created this way, making subjacency easily tested.
• Imagine moving 'the book' from 'I know the story about the book that John read.' The 'the book' might have to leap over multiple bounding nodes, creating an unacceptable sentence. The sentence is deemed ungrammatical because of the 'long-distance' movement. The principle highlights how syntactic boundaries constrain grammatical operations, such as movement.