Conceptual Dependency Theory (1969) › The Solution: Primitive Actions and Conceptual Cases
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Conceptual Dependency solved the meaning representation problem by introducing a small set of primitive actions that could be combined to represent any event. These primitives were chosen to be at the right level of abstraction: specific enough to distinguish different types of events, but general enough to capture semantic equivalence across diverse surface forms. The theory proposed approximately a dozen primitive actions, including:
- ATRANS: Transfer of abstract relationships (possession, ownership, control)
- PTRANS: Transfer of physical location (movement of objects)
- PROPEL: Application of physical force
- MOVE: Movement of a body part
- GRASP: Physical grasping of an object
- INGEST: Taking something into the body
- EXPEL: Removing something from the body
- MTRANS: Transfer of mental information
- MBUILD: Construction of new thoughts from old ones
- SPEAK: Production of sounds
- ATTEND: Focusing sense organs on a stimulus
Each action had associated conceptual cases, slots for an object or actor and for role-specific participants such as a recipient. These cases were similar to semantic roles or thematic roles in linguistics, but specifically designed for computational inference. The cases included:
- ACTOR: The entity performing the action
- OBJECT: The thing being acted upon
- TO and FROM: Direction of transfer (for TRANS actions)
- INSTRUMENT: The means used to perform the action
- RECIPIENT: The entity receiving something
- DIRECTION: Physical or abstract direction of movement
A Conceptual Dependency structure was a network connecting these primitives and cases. "John gave Mary a book" would be represented as an ATRANS action (transfer of possession) with John as ACTOR, book as OBJECT, and Mary as RECIPIENT (TO case). The structure might look like:
ATRANS
ACTOR: John
OBJECT: Book
TO: Mary
This same structure could represent "Mary received a book from John," "John passed a book to Mary," or any other paraphrase expressing the transfer of possession. The canonical form made semantic equivalence transparent.
Schank's choice of primitive actions reflected a hypothesis about the structure of human conceptual understanding: that all events could be decomposed into a small set of fundamental action types. This wasn't merely a computational convenience. It reflected a claim about how humans organize their understanding of events. By choosing primitives like ATRANS (abstract transfer) rather than domain-specific actions like "buy" or "sell," the theory captured commonalities across diverse events. A purchase, a gift, and a theft all involve ATRANS, differing only in the circumstances and motivations surrounding the transfer.
The theory also included state primitives, conceptualizations of conditions rather than events. States included physical states (like location, possession) and mental states (like knowing, wanting). A sentence like "John has a book" would be represented as a state primitive indicating possession: John is in a POSS-BY state with respect to the book. These states provided a way to represent the results of actions and the conditions that enable or trigger them.
Inference rules operated directly on Conceptual Dependency structures. The system could infer consequences of actions: an ATRANS from ACTOR to RECIPIENT implied a change in the POSS-BY state, with the RECIPIENT gaining possession and the ACTOR losing it. Causal chains could be constructed: if someone PROPELLED an object toward a location, the object PTRANSed (moved) to that location. These inference rules were built into the representation itself, making common-sense reasoning more straightforward than with predicate logic where such rules had to be explicitly stated.
The representation handled complex sentences through embedding. "John persuaded Mary to give him the book" involved multiple actions: a MTRANS (mental transfer) representing the persuasion, with the content of that transfer being another Conceptual Dependency structure (the ATRANS of the book). This recursive structure allowed the theory to represent nested events and mental attitudes.