One of the consequences of the Norman Conquest was the French influence on English spelling. Those letters which the French did not employ gradually went out of use. They were the letters æ þ ™.
New letters were introduced, such as g, j, k, q, v.
Many new digraphs and combinations of letters came into use, such as th, sh, ch, gh, ph, dg, ck, gu, qu, ouorow.
E.g. OE wiþ, ME with; OE fisc, ME fish; OE cin, ME chin; OE niht,
ME night; ME philosophie, E philosophy; OE ec™,ME edge; OE loc, ME lock; OE gæst, ME guest; OE cwēn, ME queen; OE hūs, ME hous, E house; OE nū, ME now.
Note. There was a tendency to use ow at the end of a word and ou in other positions.
It became usual to mark the length of a vowel by doubling it, especially in closed syllables.
Thus ee and oo were used to denote [ē] and [ō].
E.g. OE swēt, ME sweet, E sweet;
OE ™ōd, ME good, E good.
Sometimes the sound [ē], chiefly in French borrowings, was denoted by the digraphs ie or ei.
E.g. ME chief < OF chef; ME deceiven (E deceive) < OF deceveir.
Many letters changed their signification.
The letter u, for instance, which had denoted only one sound in OE, [u], was employed, after the French fashion, to denote also the labial front vowel [ü] formerly expressed by y. E.g. bysi™, ME busy. The corresponding long vowel was usually marked ui.
E.g. OE fyr, ME fuir, E fire.
The letter y came to denote the sounds [i] and [j].
E.g. OE his, ME his, hys; OE dæ™, ME day.
Note. There was a tendency to use the letter iat the beginning and in the middle of words, and the letter y at the end of a word to separate it from the next one, as there were often no intervals between words.
The letter cbegan to signify not only the sound [k] as in OE cōc, but also, in accordance with French usage, the sound [s] before the letters i,e,y. So, OE cēpan, for instance, could no longer be written with letter c, for it would be read [sēp•n]. It became necessary to employ the letter k in similar cases. E.g. keepen, (E keep), king.
The letter k was not frequently substituted for c in other cases. E.g. OE bōc, ME book; OE cnāwan, ME knowen, E know. Sometimes after short consonants the sound [k] was denoted by the digraph ck. E.g. OE bæc, ME back.
The letter o came to be used not only for the sound [o], but also for the sound [u]. That happened mostly in such words as ME cumen, for instance, where too many vertical lines made reading difficult. This is why words like E come, son, some have the letter o instead of u.
All these spelling changes weakened the more or less phonetic character of the OE orthography. They gave rise to fluctuations in the graphic presentations of sounds and words. In OE the sound [e:], for instance, had only one graphic equivalent, the letter ē. In ME [e:] could be represented bye, ee, ei, ie. In OE, the word fisc had only one spelling. In ME it could be written fish, fysh, fish, fisch, fyssh, fysch.