Must I explain?

I don't mind teaching English. What I do mind is trying to explain the logic behind the various rules. When a student asks, ''How come?'' I feel like rolling my eyes to the ceiling and shrugging.

How do you explain the rationale regarding the pronunciation of the following words: rough, through, though, bough, cough? How do you explain that slow converts to slowly but fast does not become fastly? Why does senator become senatorial but governor becomes gubernatorial? Why is there a silent B in comb, subtle, plumber? If we say ring, rang, rung, why can't we say bring, brang, brung? Consistency and uniformity are not the strongest characteristics of the English language.

The ''I before E'' rule prompts the following warning: ''I before E except after C'' Is a rule a teacher mentions, And its use would be quite valuable Except for the exceptions: Seismogram and heir and seine, Eiderdown and sleigh, Heinous, geisha, deify, Leisurely and weigh, Feisty, weird, and eighty-eight, Reify and either, Being, feign, and deity, Seize and beige and neither, Heiress, lei, and sleight of hand, Heighten, feint, and vein, Weir and veil and neighborhood, Sovereign and deign. ''I before E except after C''? Accept it cautiously, Or you will find yourself misled, And Einstein would agree.