A mnemonic device is one that assists the memory, from the Greek mnemon--mindful. (Mnemosyne was the Greek goddess of memory and the mother of the Muses by Zeus.)
We all know "I before e, except after c, or when sounded as "a", as in neighbor or weigh."
Fewer people know the mnemonic sentence that can help us remember the major exceptions: "Neither leisure foreigner seized the weird heights."
There is a rat in separate.
I have an independent dentist. (We also have an independent superintendent, who sings Do-Wop.)
The principal is my pal. "Principal" can also refer to a matter or thing of primary importance, or the capital sum placed at interest, due as a debt, or used as a fund, as in the principal of a loan.
A principle is a comprehensive and fundamental law, doctrine or assumption. As in, you are always true to your principles.
For the dance, your attendance is requested, just as it will be for you descendants.
A vast area was devastated.
Finally, something definite.
Like the letters you'll write on it, stationery has an "e" in it. (As opposed to stationary, or unmoving, objects.)
We're all all grateful for congratulations.
The U.S. Capitol building has a dome on it -- as do the "o"s in both words. Confusingly, Washington., D.C., is the capital of the United States.
Why? The former word comes from the Capitoleum , the temple of Jupiter at Rome that sat atop the Capitoline hill. The latter comes from the Latin capitalis, meaning chief, or principal, (derived from the Latin word caput, meaning "head"). All you have to remember is the building has a domed "o." All other meanings are with an "a."
How can you learn for sure to spell tough words, like occurrence, or accommodate? Or parallel? One good start is to pay a visit to Harbrace Chapter 18: Spelling and Hyphenation. The first seven pages are invaluable for anyone.