20 Common Grammar Mistakes That (Almost) Everyone Makes

Who and Whom

This one opens a big can of worms. “Who” is a subjective — or nominative — pronoun, along with "he," "she," "it," "we," and "they." It’s used when the pronoun acts as the subject of a clause. “Whom” is an objective pronoun, along with "him," "her," "it", "us," and "them." It’s used when the pronoun acts as the object of a clause. Using “who” or “whom” depends on whether you’re referring to the subject or object of a sentence. When in doubt, substitute “who” with the subjective pronouns “he” or “she,” e.g., Who loves you? cf., He loves me.Similarly, you can also substitute “whom” with the objective pronouns “him” or “her.” e.g., I consulted an attorney whom I met in New York. cf., I consulted him.

Which and That

This is one of the most common mistakes out there, and understandably so. “That” is a restrictive pronoun. It’s vital to the noun to which it’s referring.  e.g., I don’t trust fruits and vegetables that aren’t organic. Here, I’m referring to all non-organic fruits or vegetables. In other words, I only trust fruits and vegetables that are organic. “Which” introduces a relative clause. It allows qualifiers that may not be essential. e.g., I recommend you eat only organic fruits and vegetables, which are available in area grocery stores. In this case, you don’t have to go to a specific grocery store to obtain organic fruits and vegetables. “Which” qualifies, “that” restricts. “Which” is more ambiguous however, and by virtue of its meaning is flexible enough to be used in many restrictive clauses. e.g., The house, which is burning, is mine. e.g., The house that is burning is mine.