If you want to appear literate, you will have to avoid errors in grammar and usage. These are hardy perennials.

It’s and its If you are not a copy editor, you would be astonished to discover how many professional writers confuse the contraction it’s from the possessive its. Sometimes it’s a mere typographical error; the wrong synapse fires, and the finger hits an unintended apostrophe. Sometimes it’s just sloppiness, the product of an I-don’t-have-to-pick-up-after-myself-somebody-else-can-clean-it-up attitude. But it always looks subliterate.

Who and whom Linguists have been predicting for decades that whom is doomed. It will fade out of the language except for some stock phrases — for whom the bell tolls — and attempts at creating an archaic effect. Who will serve as both subject and object. But not while I’m alive. The most common confusion comes when who is, or ought to be, the subject of a noun clause that functions as the object of a verb or preposition. In the sentence The voters will chose whoever they think is the stronger candidate, the subordinate clause whoever is the stronger candidate must have whoever as its subject.

Subject-verb agreement Generally, phrases that fall between the subject and the verb do not, and should not, influence whether the verb is singular or plural. In the sentence The lobbyist, along with the four congressmen he is accused of bribing, is to testify at a hearing, the subject is lobbyist.

Misplaced modifiers An initial phrase that functions as an adjective, describing a person, place or thing, is assumed in English to refer to the subject of the sentence. In this one, Since their birth Nov. 19, doctors and nurses have noticed distinct differences in the babies, the ready reader will conclude that it was the babies who were born Nov. 19, not the exceptionally precocious doctors and nurses. Usually, the remedy is to place the modifier closer to the word modified: Doctors and nurses have noticed distinct differences in the babies since their birth Nov. 19.

Plurals and possessives When you drive down the street and see the charming shingle hanging from a mailbox that says The Smith’s, you can be confident that the Smiths were inattentive in English class. We do not form the plurals of singular nouns by adding ’s. If the mailbox next door proclaims The Jones’, that family is no better off. Here’s the pattern: Singular Smith Jones Plural Smiths Joneses Singular possessive Smith’s Jones’s or Jones’ Plural possessive Smiths’ Joneses’

Punctuation of clauses Compound sentences — two independent clauses separated by the coordinating conjunctions and, but or or — must be joined by a comma: He filed the story, and she began to edit it with trepidation. Compound predicates — a single subject with two or more verbs — do not require a comma: She opened the story and grimaced in alarm. Why many writers reverse these patterns is an enduring mystery.

The comma-splice run-on sentence — two independent clauses linked by a mere comma — is commonplace in British English but still deplored in American English. Use the damn semicolon; that’s what it’s for. Obnoxious pleonasms If you have been reading these dispatches, you should know better than to get me started on redundant expressions that betray the writer’s inattention to what he or she is saying: safe haven, mass exodus, free gift, advance planning, end result and a multitude of others.

Failed distinctions If you can tell the difference between imply and infer, comprise and compose, go to the head of the class. To imply is to hint or suggest. The root ply, or fold, from the Latin plicare, suggests that meaning is folded into a sentence. To infer, from the Latin inferre, to bring or carry in, is to draw the meaning out of the sentence. At your birthday, you wouldn’t mistake the action of putting a gift into a box for the act of taking a gift out of a box. Why, then, would you confuse the parallel actions of imply and infer?

Comprise means to include or contain. The alphabet comprises 26 letters. Compose means to make up on constitute. The alphabet is composed of 26 letters. The phrase is comprised of is an error at all times and in all places.

Confusion of homonyms Lead (a verb pronounced as leed) and lead (a verb pronounced as led) are homographs; they are spelled the same but have different pronunciations and meanings. Writers frequently use lead as the past tense of to lead, and the spell-check function on your computer will not touch it. Lead (a noun pronounced as led) and led (the past tense of lead) are homophones; they are pronounced the same but have different spellings and meanings. Don’t bother me for an exhaustive list. Go to Alan Cooper’s Homonyms.

Persistence in superstitions If you are still contorting sentences to keep from leaving prepositions at the end, or to move adverbs from their rightful place between the auxiliary and the main verb, or to avoid split infinitives, or to keep since from meaning because, just stop it. These are all superstitions of usage that have been repeatedly exploded. Buy Garner’s Modern American Usage, read the entry on Superstitions, and clean up your act.