VI Spelling
The spelling of English words is not fixed and invariable, nor does it depend on any other authority than general agreement. At the present day there is practically unanimous agreement as to the spelling of most words. In the list below, for example, rime for rhyme is the only allowable variation; all the other forms are co-extensive with the English language. At any given moment, however, a relatively small number of words may be spelled in more than one way. Gradually, as a rule, one of these forms comes to be generally preferred, and the less customary form comes to look obsolete and is discarded. From time to time new forms, mostly simplifications, are introduced by innovators, and either win their place or die of neglect.
The practical objection to unaccepted and over-simplified spellings is the disfavor with which they are received by the reader. They distract his attention and exhaust his patience. He reads the form though automatically, without thought of its needless complexity; he reads the abbreviation tho and mentally supplies the missing letters, at the cost of a fraction of his attention. The writer has defeated his own purpose.
Words Often Misspelled accidentally
advice
affect
believe
benefit
challenge
coarse
course
criticize
deceive
definite
describe
despise
develop
disappoint
dissipate
duel
ecstasy
effect
embarrass
existence
fascinate
fiery
formerly
humorous
hypocrisy
immediately
impostor
incident
incidentally
latter
led
lose
marriage
mischief
murmur
necessary
occurred
opportunity
parallel
Philip
playwright
preceding
prejudice
principal
principle
privilege
pursue
repetition
rhyme
rhythm
ridiculous
sacrilegious
seize
separate
shepherd
siege
similar
simile
too
tragedy
tries
undoubtedly
until
villain
Note that a single consonant (other than v) preceded by a stressed short vowel is doubled before -ed and -ing: planned, letting, beginning. (Coming is an exception.)
Write to-day, to-night, to-morrow (but not together) with a hyphen.
Write any one, every one, some one, some time (except in the sense of formerly) as two words.