The problem of the relationship between language and thought is an ancient one and it is still contested. At one extreme some authors, for example Müller (1887), have maintained that language and thought are identical and that thinking cannot occur without language. At the other extreme, the two are regarded as entirely independent: language makes no significant contribution to thinking; thus Berkeley, quoted by Cohen (1954), believed that words are an impediment to thinking. A third view admits a reciprocal relationship between the two. This notion was supported by Sir William Hamilton (quoted by Black, 1962) when he compared the relationship between language and thought to that between an arch of masonry and a tunnel: '... every movement forward in language must be determined by an antecedent movement forward in thought, still, unless thought be accompanied at each point of its evolution by a corresponding evolution of language, its further development is arrested'. This idea that language and thinking are mutually dependent was taken up by Révész (1954) in a symposium on the subject. He argued that thinking and speech cannot be identical because their ontogenesis is different and because words are often inadequate expressions of thoughts and emotions, but nor can they be distinct and independent processes because there are many congruities between them and because disturbances of speech and thought often go together. Therefore, Révész says, they must be two distinct processes which are dependent upon one another.