Appendix A: Lenition

This list is not meant to take the place of a more precise treatment, such as you will find in GMW 14-21. It only gives a guide to the relative frequency of lenitions in PPD1, and this must be read with the memory that "real" elisions may be confidently restored at this period, whereas "analogous" lenitions may often be disguised by the conservatism of Medieval Welsh spelling. Other people's counts will vary.

Cause of Lenition		Occurrences
1	a preverbal or relative	84
2	ei 'his' or infixed form	39
3	prepositions am, ar, o, trwy, tros, i, hyd	35
4	feminine nouns after article	24
5	ni, na	15
6	subject or object after verb	15
7	subject or predicate after 'to be'	9
8	noun after positive adjective	8
9	conjunctions pann, tra, yny	8
10	yn adverbial	7
11	some numbers (especially '2')	7
12	dy	6
13	'th	6
14	pa	6
15	adjective after feminine singular	5
	miscellaneous	20

A very useful guide to Modern Welsh mutations, and therefore (broadly) to Medieval Welsh mutations:

D. Geraint Lewis, Y Treigliadur (Gomer Press 1993)

Despite the title, it is in English and Welsh.