Perhaps it may not be too much to hope that intelligent readers will admit that much of what I have said has at least some prima facie likelihood. No one who knows much about the history of any language will think it probable that Welsh has remained unchanged for some eighteen hundred years. And when I assert that the changes have been as great as those which have transformed Latin into French, and that therefore the Welsh dictionary, in the hands of a person not specially trained to use it, is worthless as a key to the interpretation of British names of the first or second century, it will perhaps be acknowledged that the statement is not intrinsically incredible. But the question may reasonably be asked, what are the means by which philologists claim to be able to interpret some of these ancient names? There is no surviving British literature of the period of Roman rule; how then is it possible to discover what the British language of this early date was like? The question deserves an answer, and I will endeavour to give it, so far as can be done without presupposing more philological knowledge than ordinary educated readers may be expected to possess.
In the first place, the history of the Welsh language for many centuries back can be traced by means of its extensive literary remains. When we compare the forms of Welsh words as they appear in the oldest literature with those in which they are now current, we discover that many of the sounds of the language have undergone certain uniform changes. For instance, if a modern Welsh word contains a b, d, or g between vowels or at the end, we know that those sounds are alterations of an original p, t, or k respectively. Again, if a word in the oldest known Welsh contained an intervocalic or final b, m, d, or g, then we find (if the word has come down into the modern language) that the consonant has not remained unaltered: b and m have become v (written f), d has become dd (pronounced like th
