Why these particular mistakes are so common
Nearly every entry on this list involves homophones — words that sound identical when spoken but are spelled differently and mean different things. Because they sound correct out loud, they slip past a writer's ear, and because they are spelled correctly as standalone words, they slip past a spell-checker too.
The fastest way to catch them yourself
The substitution test used throughout this list — mentally expanding a contraction back to its full words — catches the majority of these errors in seconds. Reading a sentence aloud also helps, since your ear will often notice an odd rhythm even when your eye skips right past a typo.
When a "rule" is actually more flexible than it sounds
Some traditionally taught rules, like never ending a sentence with a preposition or never splitting an infinitive, are treated as much more flexible by modern style guides when the alternative sounds stiff or unnatural. The mixups above are different — they change the literal meaning of the sentence, which is why they are worth getting right even in casual writing.
Frequently Asked Questions
Does spell-check catch any of these?
Rarely. Spell-check flags misspelled words, but "there" and "their" are both spelled correctly — the mistake is a word-choice error, not a spelling error, so basic spell-check tools miss it entirely.
Is "less" always technically wrong for countable nouns?
By the traditional rule, yes, though the distinction is loosening in casual speech. Formal or professional writing is still safer sticking to fewer for countable items.
Is ending a sentence with a preposition actually incorrect?
No — most modern style guides consider it perfectly acceptable when the alternative phrasing sounds awkward or overly formal.
What is the single fastest way to catch these before hitting send?
Read the sentence back and mentally expand any contraction to its full two words — if "it is," "you are," or "they are" still makes sense in that spot, the apostrophe version is correct.