In order to understand bird flight, we have to understand aerodynamics; only then does the structure of feathers and the different shapes of bird's w… - David Marr

The abstract properties of this mapping are defined precisely, and its appropriateness and adequacy for the task at hand are demonstrated.

A representation is a formal system for making explicit certain entities or types of information, together with a specification of how the system does this. And I shall call the result of using a representation to describe a given entity a description of the entity in that representation.

[If] we can experimentally isolate a process and show that it can still work well, then it cannot require complex interaction with other parts of vision and can therefore be understood relatively well on its own.