It is important to observe that the combinations st, sc, sp are not allowed to alliterate with each other or with words beginning with s not followed by a consonant, but st can alliterate only with st, sc only with sc, sp only with sp; thus spere and scyld, stillan and springan, sǣ and styrman do not count as alliterations. The invariable practice is seen in the following lines:—
hēt strḗamfare stíllan, stórmas réstan. An. 1578.
he scḗaf þā mid þam scýlde, þæt se scéatt tōbǽrst
and þæt spére spréngde, þæt hit spráng ongḗan. Byrhtnoth 136–7.
In later times this rule was not so strictly observed. The metrical Psalms alliterate sc with s and sw with s, as
hi hine him sámnuncga scéarpum strḗlum. Ps. lxiii. 4.
on þī́ne þā swī́ðran, ond þe ne scéaðeð ǣ́nig.Ps. xc. 7.
but sp and st do not alliterate with each other or with s. In Ælfric all these combinations of consonants alliterate indifferently with each other or with s + another consonant or with simple s, as in
wið þā́m þe hēo beswī́ce Sámson þone strángan.Ælfr. Judges 308.
Sometimes in Ælfric the alliterating letter does not stand at the beginning of the word,