I. The facts about the behaviour of fricatives in Old English in relation to surrounding segments are well known; but these facts (and some others) illustrate some interesting general principles that seem not to have been thoroughly discussed. A classic formulation of the data is that of Sweet (1953: 3):… f and s, in addition to their modern values, could represent respectively the sounds of v and z, letters which were not normally used in O.E. These three letters, f, s, p, had the sounds of f, s, and th in thin (‘breathed’ or ‘voiceless’) initially and finally in accented words; next to ‘voiceless’ consonants (such as p, t); and when double; … They had the sounds of v, z, and th in then (‘voiced’) when single between vowels, or between a vowel and another ‘voiced’ sound (such as l, r, m, n)….To generalize this, we might say that in Old English fricatives were voiced between sonorants, and voiceless if geminate or contiguous to a major boundary, or in clusters with voiceless obstruents (of which as we will see geminates are a special case). One way of capturing these facts would be a rule which states simply that fricatives are voiced between sonorants, and voiceless elsewhere.