| Aitchison,Carter, A Geography of the Welsh Language, 1994 | :: | 1 |
| Chomsky, Syntactic Structures, 1957 | :: | 40 |
| Fishman, Reversing Language Shift, 1991 | :: | 1 |
| Hawkins,Gell-Mann, The Evolution of Human Languages, 1992 | :: | 16 |
| Kroch, Reflexes of grammar in patterns of language change, 1989 | :: | 29 |
| Lightfoot, The development of language: Acquisition, change and evolution, 1999 | :: | 41 |
| Niyogi,Berwick, Evolutionary Consequences of Language Learning, 1997 | :: | 29 |
| Nowak,Komarova,Niyogi, Computational and evolutionary aspects of language, 2002 | :: | 49 |
| Office,UK, Census: Report for Wales, 1991 | :: | 1 |
| Withers, Gaelic in Scotland 1698-1981: The Geographical History of a Language, 1984 | :: | 1 |