Rule 7. In simple derivatives a single final consonant following a single vowel in a syllable that receives an accent is doubled when another syllable beginning with a vowel is added.
Rule 8. When accent comes on a syllable standing next to the last, it has a tendency to lengthen the vowel; but on syllables farther from the end, the tendency is to shorten the vowel without doubling the consonant. For example, na′tion (a long), but na′tional (a short); gram′mar, but grammat′ical.
Rule 9. Silent e at the end of a word is usually dropped when a syllable beginning with a vowel is added. The chief exceptions are words in which the silent e is retained to preserve the soft sound of c or g.
Rule 10. Plurals are regularly formed by adding s; but if the word end in a sibilant sound (sh, zh, z, s, j, ch, x), the plural is formed by adding es, which is pronounced as a separate syllable. If the word end{s} in a sibilant sound followed by silent e, that e unites with the s to form a separate syllable. Examples: seas, cans; boxes, churches, brushes; changes, services.
Rule 11. Final y is regularly changed to i when a syllable is added. In plurals it is changed to ies, except when preceded by a vowel, when a simple s is added without change of the y. Examples: clumsy, clumsily; city, cities; chimney, chimneys. We have colloquies because u after q has the value of the consonant w. There are a few exceptions to the above rule. When two i's would come together, the y is not changed, as in carrying.
Rule 12. Words ending, in a double consonant commonly retain the double consonant in derivatives. The chief exception is all, which drops one l, as in almighty, already, although, etc. According to English usage other words ending in double l drop one l in derivatives, and we have skilful (for skillful), wilful (for willful), etc., but Webster does not approve this custom. Ful is an affix, not the word full in a compound.
EXCEPTIONS AND IRREGULARITIES.
1. Though in the case of simple words ending in a double consonant the derivatives usually retain the double consonant, pontific and pontifical (from pontiff) are exceptions, and when three letters of the same kind would come together, one is usually dropped, as in agreed (agree plus ed), illy (ill plus ly), belless, etc. We may write bell-less, etc., however, in the case of words in which three l's come together, separating the syllables by a hyphen.
2. To prevent two i's coming together, we change i to y in dying, tying, vying, etc., from die, tie, and vie.
3. Derivatives from adjectives ending in y do not change y to i, and we have shyly, shyness, slyly, etc., though drier and driest from dry are used. The y is not changed before ship, as in secretaryship, ladyship, etc., nor in babyhood and ladykin.