RULES REFERRING TO THE FORMATION OF THE PARTICIPLES OF VERBS.

I.

Verbs which terminate in e take d alone when forming the past tense, and omit the e when adding ing for the present participle; as: hope, hoped, hoping.

Dye, eye, hoe, keep the e; as: dyeing, eyeing, hoeing.
And see Rule II.

[The rule for the spelling of verbs in ieve and eive may be usefully placed here: when c precedes the troublesome vowels, spell them ei; if not, ie.

Examples: conceive, deceive, perceive, receive. But achieve; believe, relieve; grieve, reprieve, retrieve; thieve. Also note verbs in ceed and cede. Exceed, proceed, succeed; but accede, concede, precede, recede.]

II.

Verbs ending with a, ee, o, x, ow, aw, ew, or with a double letter, always retain the same when ed or ing is added; as: huzza, huzzaed, huzzaing; free, freed, freeing; flow, flowed, flowing; vex, vexed, vexing.

III.

Monosyllables which terminate with a single consonant, preceded by a single vowel, require the doubling of the consonant when ed or ing is added; as: pen, penned, penning.

Sometimes the d is changed into t; as: dipt (for dipped).

IV.

Verbs ending with two consonants do not double the last when adding ed or ing; as: print, printed, printing.

V.

Verbs which terminate in a single consonant preceded by two vowels (making in pronunciation a single vowel, usually long) or a diphthong, do not double that consonant when ed or ing is added; as: clean, cleaned, cleaning.

Sometimes the d is changed into t; as: knelt (for kneeled).

VI.

In verbs of more than one syllable, ending in a single consonant, preceded by a single vowel (or vowel sound), the doubling of the consonant is always required on adding ed or ing, when the accent is on the last syllable; as confer, conferred, conferring.

Except chagrin, chagrined, chagrining; invalid, invalided, invaliding.

VII.

In verbs not accented on the last syllable, the doubling of the final consonant does not take place when ed or ing is added; as profit, profited, profiting.

VIII.

But verbs ending in preceded by a single vowel (or vowel sound), generally double this consonant, even when the accent is not on the last syllable; as: travel, travelled, travelling; impel, impelled, impelling.

Parallel more commonly takes single : paralleled, paralleling.

Verbs ending in c (for older ck) take ck before the endings; as: traffic, trafficked, trafficking.

Also two in s: bias, biassed, biassing; nonplus, nonplussed, nonplussing. But bias often keeps single s.

And some others; as: periwig, periwigged, periwigging.