In a field like Africa it is reasonable to hope for some assistance from linguistic data for the general study of prehistory. In fact there is a real temptation to use material of this kind in such a way that the results cannot be verified, or, to put it more baldly, to make guesses that are no better than other guesses. Clearly the serious investigation of the prehistory of Africa demands something more than speculative hypotheses, and for this reason it is essential that any conclusions drawn from linguistic information shall be based on a firm basis of codified data.