Some words and phrases are so similar to other words and phrases that it is easy to mix them up. For example, “wait on” and “wait for.” (That one has a page all to itself on this site.) Here are a few others:
further / farther — “Further” means “in addition” or “more deeply”; “farther” means “more distant.” “Further” should be used for abstract nouns or concepts. It is not a comparative; that is, there is no “fur,” and “further” is not more “fur” than something else. It means “in addition” or “in extension.” “Farther,” on the other hand is a comparative. It means “more far,” and is reserved for matters in the physical world. The Ford Motor Company recently formed an advertising campaign around the slogan “Go Further.” In a Ford? Few have raised hell about it, which indicates that most Americans do not know about the difference, or do not care. The two terms have been used interchangeably for decades, if not longer, and sometimes by careful and educated writers. If you care about the difference (and I believe you should), remember: To “go further” means to delve more deeply into the subject being discussed, to elaborate. To cover more distance, one needs to “go farther.”
continuous / continual — “Continuous” is unceasing, like the continuous ringing of a fire alarm. “Continual” occurs frequently, but is intermittent, as in “I am proud of your continual high performance in Math.” A river flows continuously (without interruption); a spoiled child whines continually (very frequently).
effect / affect — As nouns, “effect” means the result of some action, where as “affect” means an observable emotional response of a person to interactions with others. As verbs, “effect” means to bring about; “affect” means to have influence on or over something. Simply put, they are two different words: Anyone paying attention to his or her usage should have no trouble avoiding this mistake.
inoperative / inoperable — “Inoperative” means “out of order,” “not working.” “Inoperable” refers to a condition that can not be remedied by a surgical procedure. If someone says that the drink machine is “inoperable,” it means that whatever is wrong with it cannot be cured by the intervention of a surgeon: probably not what the person had in mind.
uninterested / disinterested — “Uninterested” means bored, unconcerned or impassive with respect to something. “Disinterested” means neutral, or having no stake in the outcome of something. We hope our football referees are disinterested in the game, but we certainly do not want them to be uninterested in it.
ingenious / ingenuous — “Ingenious” is clever or imaginative. “Ingenuous” is naive, gullible, not at all clever. The words are not quite antonyms, in that “ingenious” applies to plans, actions, maneuvers and the like; “ingenuous” describes the artless quality in a person. (Curiously, we also have “disingenuous,” which means insincere, usually by feigning ignorance.)
likely / liable — “Likely” means “probable.” In your father’s or grandfather’s schools days, “liable” meant exclusively “legally answerable or obligated.” It was never to be used to describe the possibility of some future event. A person who was liable to do something was obliged to do it. It was wrong to write, “That moonshine still is liable to blow up!” unless there was some obligation on the part of the “still” to explode. Another word, “apt,” enters the discussion. It means “qualified,” “capable” or “ready.” A student who is apt to take a certain course has met all the prerequisites for that particular study. “Apt to” does not mean “likely.” In recent times, “liable,” “likely” and “apt” have come to be used almost interchangeably. Some authorities even accept them as synonyms with slightly differing shades of meaning. Personally, I regard that as adding confusion to an already muddled subject. Simplicity would counsel you to use “likely” for probable, “apt” for qualified or ready, and “liable” for obligated or obliged.
barbarous / barbaric — historically, these words have been used interchangeably, but often with a subtle differentiation: “barbarous” emphasizes the crudity of the person, group, tradition or action; “barbaric” emphasizes its cruelty. Thus, a “barbarous” tribe is uncivilized, whereas a “barbaric tribe” is bloodthirsty and cruel. Historically, the words evolved on parallel paths, and so this distinction is more a modern effort to give different meanings to different words. It seems like a good idea.
immoral / amoral — English has thousands of words that can take prefixes to modify their meanings. For example, “moral” means adhering to acceptable rules and standards of conduct. “Immoral” negates it in the same way that “im-” turns “possible” into “impossible.” “Amoral” simply says that morality is not involved. An “amoral person” does not adhere to behavioral norms because he or she neither acknowledges nor adopts them. Such a person simply has no morals, for good or for ill. For this reason, “amoral” is often confused with “immoral” in the context of a normative society. In general, the prefix “a-” means “without.” A common example is “apolitical,” which means that no political positions are involved.
bring / take — Try to avoid this mistake. These two verbs involve carrying something, and their difference involves the point of view of the person using the word. If the carrying is towards or along with the utterer, then it is “bring“; If the carrying is away from the utterer, then it is “take.” The mistake most often happens when a departing person is asked to “bring” something with him (meaning “take”).