What are the trickiest rules in English grammar pertaining to commonly used words?

Words ending in “on”: This is a tricky one. If the singular noun ends in “on,” you make it plural by removing the “on” and adding an “a.” For example, criterion turns into criteria. Words ending in “o”: This is another situation with more than one rule to follow. read less

Here are some tricky rules in English grammar related to commonly used words: Affect vs. Effect: "Affect" is usually a verb, meaning to influence or produce a change, while "effect" is typically a noun, referring to the result of a change. Their, There, They're: "Their" is a possessive pronoun, "there" indicates a place, and "they're" is a contraction for "they are." Your vs. You're: "Your" is a possessive pronoun, indicating ownership ("your book"), while "you're" is a contraction for "you are." Its vs. It's: "Its" is a possessive pronoun, indicating ownership ("the dog wagged its tail"), while "it's" is a contraction for "it is" or "it has." Who vs. Whom: "Who" is used for the subject of a sentence, while "whom" is used for the object. However, "whom" is less commonly used in modern English. Then vs. Than: "Then" refers to a specific time or sequence of events, while "than" is used for making comparisons. Farther vs. Further: "Farther" refers to physical distance, while "further" often refers to a figurative or metaphorical distance or advancement. Lay vs. Lie: "Lay" requires a direct object and means to put or place something down ("lay the book on the table"), while "lie" does not take a direct object and means to recline or rest ("lie down on the bed"). Fewer vs. Less: "Fewer" is used with countable nouns ("fewer apples"), while "less" is used with uncountable nouns ("less water"). Me, Myself, and I: "Me" is an object pronoun ("She gave it to me"), "myself" is a reflexive pronoun used when the subject and object are the same ("I did it myself"), and "I" is a subject pronoun ("I went to the store"). read less