The computer and natural language is a sub-domain of computer science in which one of the major aims is to imitation of man, focusing on two topics: psychology and linguistics. If we wish the machine to do something, we must tell it what to do and it must be able to understand us. The easiest way to tell a computer what to do is to give it a program to run. "Humans, if they are machines at all, are vastly general-purpose machines and what, is most important, they understand communications couched in natural language." Work must be done for a machine to understand natural language. "Man's capacity to manipulate symbols, his very ability to think, is inextricably interwoven with his linguistic abilities." A machine must be able to extract semantic content from the messages impinged upon it, adopt a syntactic structure of a visual scene and adopt a certain conceptual framework. The question of what comprises a visual symbol is in question. The developer defines the elements of the machines primitive vocabulary. Robert Lindsay said, "high quality translations could be produced by machines supplied with sufficiently detailed syntactic rules, a large dictionary, and sufficient speed to examine the context of ambiguous words for a few word in each direction."