A FEW CONTRASTS

Since vs. Until: beginning vs. end Since: tells when something (an action or "interim") BEGINS (duration or repetition). If there is a verb after since, it is in a past tense. The verb in the main clause is in a perfect tense. (The action or "interim" ends at the present (if the verb is present perfect) or at a previously-identified time in the past, if the verb is past perfect) I've been sick since I got here. (It STARTED then) I'd seen him three times since Tuesday. (The period in question STARTED Tuesday) Until: tells when something ENDS (duration) The verbs can be in any tense. I will study until 10pm. (I will STOP at 10) I kept falling down until I got my new boots. (I STOPPED when I got them) Since vs. Until: WITH NEGATIVE VERBS (in the main clause): The use of since and until with negative verbs can be confusing, because in effect what is meant is that the ABSENCE of someting starts or ends. In other words: Since with a negative verb: I haven't seen her since Tuesday. (The period during which I did NOT see her BEGAN Tuesday and extended until now. It's possible that I do see her now. I probably did see her Tuesday.) It was Tuesday. I hadn't seen her since I left. (The period during which I did NOT see her BEGAN at time I left and extended until Tuesday (in the past.) I probably did see her before I left, and again Tuesday.) Until with a negative verb (usually "punctual" verbs): I didn't start studying until 10pm. (I STOPPED NOT studying at 10; ie. I started at 10) I didn't fall down until I got to the bridge. (I STOPPED NOT falling down at the bridge; ie, I fell there.) NOTE: With verbs of duration, the meaning with a negative verb can be ambiguous -- although intonation helps in spoken English. For this reason, they may be rarer, especially in written English: I didn't study until 10: (EITHER: I did NOT stop studying AT 10. = I studied until 8 or 11 or some other time. - (intonation important for this one) OR: I stopped NOT STUDYING at 10. = I began to study at 10, which was late.)

Since with superlatives "main" clause (actually a relative clause) implied Since: normally introduces an adverb clause (or adverb or prepositional phrase) telling us when the action referred to in a main clause BEGINS (or the interim during which the action occurs begins) (duration or repetition). The verb in the main clause is in a perfect tense. (The action or "interim" ends at the present (if the verb is present perfect) or at a previously-identified time in the past, if the verb is past perfect) I've been sick since I got here. (It STARTED then) I'd seen him three times since Tuesday. (The period in question STARTED Tuesday) However, it can also be used (informally?) with expressions like superlatives or words like "first", without the main clause. The expression with since refers to the beginning of a period of "inferior" examples: (since identifies the most recent equally superior/novel example, which is followed by a period of "inferior" examples, ending with this "superior" or "novel" one.) The reference to this period (which would be the main clause including a perfect tense verb) is implied; the verbs actually in the sentence are determined by the rest of the sentence. The phrase or clause introduced by since immediately follows the noun with the superlative modifier, because the implied main clause would actually be a relative clause modifying that noun : This might be the funniest movie since "Duck Soup". ( = the funniest movie that has been made since ..) That was his first date since he was in high school. ( = the first date he had had since ..) They will be the most sweeping changes since the New Deal. ( = changes that will have been made since ..) He thinks it's the best thing since sliced bread. ( = the best thing that has been invented since sliced bread)

Since vs Ago past time named (beginning of period) vs. specific past time by calculation Since: points to the beginning of a PERIOD OF TIME. Since is followed by a specific past time. It usually requires a perfect verb in the main clause: I've been sick since I got here. period of time: arrival -> now I've seen him three times since Tuesday. period of time: Tuesday -> now Ago: points to a SPECIFIC PAST TIME, by telling us how far back in time to count from the present. Ago is preceded by a number or amount of time. It usually requires a past-tense verb: I was sick 3 weeks ago. specific past time: Jan. 10 (if this is Jan. 31) I met him a long time ago. specific (?) past time: many years before now NOTE: Therefore, it's possible to have both in the same phrase (Although this may seem strange to some native speakers). The since would indicate that we're talking about a period of time previous to the present time, and the ago would indicate the specific time when that period begins: I've been sick since three days ago specific past time: three days ago = Sunday (if this is Wednesday) period of time: since three days ago = three days ago (Sunday) -> now

For vs Ago period of time vs. specific past time For: indicates a PERIOD OF TIME (with no reference to WHERE in time that period is located). For is followed by a number or amount of time. The rest of the sentence tells the time, which can be past, present, future, or anything. I've been sick for three days. I'd stayed for several months. I usually sleep for a long time. period of time only Ago: indicates a SPECIFIC PAST TIME, by telling us how far back in time to count. Ago is preceded by a number or amount of time. It usually requires a past-tense verb: I was sick 3 weeks ago. specific past time: Jan. 10? I met him a long time ago. specific (?) past time: many years before now

Since vs For specific past time vs. number or amount of time Since: points to the BEGINNING of a period of time. Since is followed by a specific past time. It usually requires a perfect verb in the main clause: I've been sick since I got here. period of time: arrival -> now I've seen him three times since Tuesday. period of time: Tuesday -> now For: indicates the LENGTH of a period of time (with no reference to WHERE in time that period is located). For is followed by a number or amount of time. The rest of the sentence tells the time, which can be past, present, future, or anything. I've been sick for three days. I'd stayed for several months. I usually sleep for a long time. period of time only

Since vs From end of period understood vs. end of period identified Since: The end of the period is not mentioned, but understood to be "now" or an established past time. The main clause usually requires a perfect verb. Focus is on the DURATION OF THE ENTIRE PERIOD: I've been sick since I got here. period of time: arrival -> now I'd seen him three times since Tuesday. period of time: Tuesday -> then From: also identifies a period of time, by identifying the beginning of the period of time (a specific past time), but it focuses primarily on the BEGINNING (rather than the entire period); the END of the period must be either : a. specifically stated (with to, until, or through ) I was sick from Monday until Wednesday b. identifiable by calculation (analagous with ago*) I will go 3 weeks from now. They will be here a month from yesterday. c. alluded to, but left open-ended I hope to feel better from now on. or d. unimportant. (usually followed by a word like beginning or start , rather than a specific time) I knew from the beginning that there would be a problem. *Here, from functions as the flip side of ago, in the sense that as ago identifies a past time by telling us how far back in time to count from the present, from can identify a future time by telling us how far forward to count from a specific time. Note that with from , the point at which we begin counting must be identified; with ago , it is assumed. I went 3 weeks ago. I will go 3 weeks from now.

Until vs By looking forward vs. looking back Until: tells when something ends (duration). The focus is on THE ACTION that ends. Until is followed by specific time. I studied until 10pm. (I STOPPED at 10) I kept falling down until I got my new boots. (I STOPPED falling when I got them) By: tells when something is completed. It focuses on THE END and looks back. (completion or duration) By is also followed by a specific time. He will know everything by then. By 1963, he had been studying for 6 years. or establishes a deadline for something to be completed: Please return this by 10 pm tomorrow. EXAMPLES: Study this by tomorrow. (deadline. All I care is that you complete it before tomorrow) Think about this until tomorrow. (duration. Start now and continue. Stop tomorrow.) He had been studying for 6 years by 1963. (completion. situation established in 1963, looking back) He studied from 1957 until 1963. (duration that stops in 1963, looking forward)

For vs During vs While amount of time (how long?) vs. noun vs. clause (when?) For: indicates the length of a period of time (Answers the question: HOW LONG? -- with no reference to WHERE in time that period is located). For is followed by A NUMBER OR AMOUNT OF TIME. The rest of the sentence tells the time, which can be past, present, future, or anything. I've been sick for three days. I'll stay for several months. I usually sleep for a long time. During : is followed by A NOUN referring to a period of time (NOT a number or amount of time, and NOT a clause or gerund). (Answers the question: WHEN?) The rest of the sentence tells the time, which can be past, present, future, or anything. I will go there during my vacation. They are very busy during election years. While: is followed by A CLAUSE OR PARTICIPIAL PHRASE, referring to a period of time. (When?) I went there while I was on vacation. They are very busy while elections are going on. I fell while skiing.