The way that I remember it
Any little trick to remember a correct spelling is worth keeping in mind.
A colleague reports that when she's trying to remember which is correct, "taller than I" or "taller than me," she just trusts her instinct. She trusts her instinct to be wrong, that is. "Taller than I" just doesn't sound right to her, and so she knows that it is.
Hey, whatever works.
When it comes to mastery of the language, there are no dumb mnemonics. Any little trick that works is worth remembering, especially when it comes to spelling. Mnemonic (it rhymes with demonic, and the "m" is silent) comes from Greek and means a memory device.
Go a-Googling for "spelling mnemonics" and you'll find that legions remember "A rat in the house might eat the ice cream" when they want to spell arithmetic. (Who knew that one was so hard?)
Stationary and stationery are often confused – that is, people have trouble remembering which spelling goes with which of two very different concepts. Stationary is the adjective meaning "fixed, not moving." Stationery is paper goods and shares with paper a long "a" and unstressed "e." That leaves stationary to be the one that does not refer to paper.
The two sound-alikes share some roots, however. Station, meaning "the place one normally occupies," goes back to 1280 and comes from the Latin word for "stand." A stationer was one who sold items (books and papers) from a fixed location – a station – as contrasted with roving peddlers.
Complementary and complimentary are another pair of words that are hard to keep straight because of their common ancestry but divergent meanings. For colors that go together well, complementary is the right word.
"Complimentary tickets" are those sent "with [someone's] compliments," that is, some little note along the lines of, "Hope you enjoy the show – Bestregards," etc.
My trick for keeping these two straight was to remember that complementary colors "complete" each other; the long "e" was the key thing to keep in mind. But a little digging I did the other day turned up the knowledge that both words come from complete.
Compliment came to English via French from the Italian complimento, "expression of respect and civility." This Italian word, I see in the Online Etymology Dictionary, came from Latin and expressed the notion of "completing the obligations of politeness." This idea shows up in novels as "Do give your parents my very best regards" but in real life has latterly morphed into something along the lines of "Say hi to your folks for me."
I think I have these two adjectives straight at this point, but if I didn't, I might seize upon the vowels in civility and connect all those "i's" with the "i" of complimentary.
Note how the so-called long vowels, the ones that "say their own names," as we learned in school, are easier to keep straight than the short or unstressed vowels, the source of much of the grief in English spelling. Is it correspondence or correspondance? It's the former, but nothing in the pronunciation is of any help at all. "You just have to memorize it!" I can hear the entire corps of my English teachers chorusing as one.
My dad used to have a one-word spelling test for prospective new members of his team at work: separate. Experience had shown him that anyone who could get that middle "a" right was likely to work out well.
Knowing this made me feel I'd better be sure I got separate right myself. I looked deep into the word and could almost see the word pair. "You wouldn't want to separate a pair," I told myself mnemonically.
Dumb, I know, but hey, whatever works.