“Who do you want to speak with?” is doubly incorrect: Can you spot the two mistakes? One is grammatical: “Who” is the nominative form of the interrogative pronoun; “whom” is the correct form for the object of a preposition, which is the requirement here.
Granted, “Whom do you want to speak with?” sounds strange and ugly. That may be the fault of the second error in the sentence, which is one of syntax and rhetoric: Do not separate the preposition in a prepositional phrase from its object; don’t stick it at the end of the sentence, down by the period or question mark.
Ending a sentence with a preposition is, in a phrase attributed to Winston Churchill, “the sort of nonsense up with which I will not put!” (Evidently, he did not really say that. See this link for more information.) As for using the nominative case when the objective case is required, or vice-versa, see Keeping Subjects and Objects in Line. Our focus at this moment is on error number 2, the incorrect placement of prepositions.
Teachers of ESL (English as a Second Language) have long confronted having to explain why English prepositions sometimes seem to float around without any objects. They tell their students, “These prepositions are really just parts of the verb.” For example, “tear down” is not a combination of the verb “tear” with a prepositional phrase that starts with “down,” nor is “down” some sort of adverb, telling how the tearing occurred. No, “tear down” means something different from its two word parts; it means to demolish, dismantle, disassemble, or destroy. “Tearing” is not involved, really, at least not necessarily, and “down” does not describe how the verb acts. At most, it merely depicts the outcome, brought about by the force of gravity on whatever is being demolished. Though capable of being either an adverb or a preposition, “down” in this case is neither. It makes imminently better sense to consider the verb to be “tear down” and the item demolished to be its direct object.
Now, it is possible to concoct a sentence in which the verb would be “tear” and “down” would introduce a proper prepositional phrase: “Watch the girl tear down the street on her bicycle.” But that is furlongs away from the sense of destroying something!
Not persuaded? Then consider “tear up.” Suppose you receive some junk mail, which you just toss away without reading it. If you “tear up” the junk mail first, does it convey any sense of direction? Is it the opposite of “tear down”? In the same vein, in the phrase “tear off,” the “off” is part of the action, not a description for whatever noun is affected by it.
ESL instructors call these two- and three-word descriptors of action “phrasal verbs.” In this light, “put up with” is a three-word verb, not a verb + preposition/adverb + preposition/adverb. Thus, to say “That is something I will not put up with” is rhetorically correct.
Why does English do this to us? The answer goes back to Old English, and earlier to Saxon, and earlier still to Old German. German (even modern German) has a feature called “separable prefix verbs.” For example, the verb “to wake up” is “aufwachen” (from which we have “awaken.”) But in German the “auf” part separates from the “wachen” part when it is employed (other than as an infinitive) and it goes to the end of the sentence. So Bach’s Cantata Number 140 is called “Wachet Auf” because that is the form “aufwachen” takes in order to say, “Wake up y’all” (“Wachet” is a plural imperative). In English, we would say, “Wake Up!” So you see, we come by these phrasal verbs quite honestly.
Now, does that mean it’s always permissible to end a sentence with a preposition? No. A preposition that introduces a phrase, one that has an object of its own, needs to stay with its object. “Speak with” is not a phrasal verb, so “Whom do you want to speak with?” is not a syntactically correct sentence. It should be, “With whom do you want to speak?”
In general, the rule for prepositional phrases is that the preposition should come first, and then the object of the preposition (together with its adjectives and any adverbs tied to the adjectives). Keep the unit all together. Sometimes the whole phrase can be placed at different parts of the sentence, but the words of the prepositional phrase should stay together, and be introduced by the preposition. For example, “In this valley I shall stay” is correct. So is “I shall stay in this valley.” It is not correct to say, “This is the valley that I shall stay in.” If you need to use a relative clause, say “in which I shall stay.”
Three-word phrasal verbs (like “put up with” or “look down on”): the three words always go together. They are a unit: “Can you put up with that?” “Beverly can not put up with hateful politics.”
In the case of two-word phrasal verbs, some of them follow the same rule: The words cannot be separated. For example, “run into” is a two-word phrasal verb in which the two words must stay together. You can say, “I ran into John yesterday,” but you can’t say, “I ran John into yesterday.”
Most two-word phrasal verbs are separable. For example, “make up” in the sense of “invent”: “She made that story up” is perfectly acceptable. Also, one can say “She made up that story.” Either way works. There is one catch, however: If the object of the verb is a pronoun, then the separable two-word phrasal verb must be separated! “She made up the story” is fine; “She made it up” is also fine; but “She made up it” is not fine at all.
To recapitulate: (1) All phrasal verbs can be kept together, followed by their object, except separable (two-word) phrasal verbs when the direct object is a pronoun. Such a pronoun must go in between the two parts of the phrasal verb. (2) Objects of separable phrasal verbs, if not pronouns, may optionally be placed either in between the two parts of the phrasal verb, or after the phrasal verb, as if the phrasal verb were non-separable.
Remember: All three-word phrasal verbs are non-separable. Some two-word phrasal verbs are non-separable, but most are separable.
A final detail: Some phrasal verbs are intransitive; that is, they do not take a direct object. It follows that all such intransitive phrasal verbs are non-separable, as there is no object to interpose between the parts. An example is the phrasal verb “come about” either in the sense of “happen” or in the sense of “turning around,” nautically speaking: “Tell me, how did this come about?” “When the sloop reached the buoy, it came about.”
English has hundreds of phrasal verbs. Here are just a few examples of them in their respective categories:
Two-word, separable (transitive): ask out, calm down (someone), find out, hang up (the phone), look up, bring up (either to rear or to mention), keep up (continue), mix up (confuse), pass out (distribute), point out, put off (defer), set up (arrange), show off, sleep off, take off (remove), think over, turn up (adjust volume) warm up (something, as a car), wake up (waken another)
Two-word, non-separable (transitive): break into (invade), bump into (or run into), call on (as a student in class), check into (a hotel or a matter), come across (encounter), do without (something), fall apart, give up (concede), look into, stick to (concentrate on).
Three-word (always non-separable): break out in, cut down on, do away with, drop in on, go out with, meet up with, add up to, give up on, grow out of, hang up on, look forward to, run out of (have no more), warm up to (begin to feel positively disposed towards).
Intransitive (always non-separable): ask around, back off, break down (malfunction), calm down, cheer up, chip in, show up, give in or give out (quit), grow up, run away, sleep around, sleep over, log in (to sign on to a computer account), pass out (lose consciousness), shop around, take off (launch), turn up (appear), work out (exercise), warm up (get ready), wake up (awaken).