I'm sure you've noticed by now that Mandarin has no 'tense'. Like in English, we say "I wore a red T-shirt"(past tense) and "I am wearing a red T-shirt"(present tense) In Mandarin, there are no verb conjugations. Here's an example: 我穿红汗衫 can be interpreted as "I wear red T-shirts" "I am wearing a red T-shirt" or even "I wore a red T-shirt". Now, if I said: 我昨天穿红汗衫-Yesterday I wore a red T-shirt, it is obvious that the action has happened already. Tense is shown by the time being stated (e.g. yesterday) but the verb does not change. 了 does not relate to past tense, but emphasizes completed actions. Like, in the sentence 我吃了早餐(I had breakfast) there is no clear distinction on WHEN exactly I ate breakfast, but that it has been completed. Which is why it is important to add 了 but lets say your friend asked "What did you do last Friday?" you could answer: 去餐馆吃晚餐-I went to a restaurant and had dinner. There is no 'le' since the time and context is clear. 过 is for positive and negative experience. (Again, there is no clear distinction between when it has happened) 我去过日本东京- I have been to Tokyo. 我没看过这部电视节目 - I haven't seen this t.v. program. An important thing to note: 过 can be used in positive and negative sentences, whereas in the sentence 他没吃西瓜 "he didn't eat watermelon" 了 cannot be used, but 过 can. Sometimes people use them in the same way, which can cause confusion. Its better to use 过 when you're talking about experience, i.e. 她去过日本东京三次- she has been to Tokyo three times. Lets say someone asked: 你功课做了吧？-You haven't finished your homework have you? Then, you could answer: 我做过功课了-I have finished my homework.过 already shows completion, but its also appropriate to use 了 here, since 了 emphasizes the whole action being complete. There are other words to show completion i.e 到，完，: 找到 -to have found, 完literally: to finish, 我吃完了- I have finished eating. And even 好 as in, 我买好了 - I have already bought[that/it].

That, sir, is a matter of diligent study.

hi, see here: http://www.italki.com/answers/question/114959-1-1-2.htm. 过 means an "experience". it's sth. happened in the past yes, but it's not only that, it usually has sth. to do with what you are talking about right now. -跟我一起去看《泰坦尼克号》吧。 -我看过，不想看了。 了 means "a change of state". A is not true before time T, then it becomes true. so before T, "没 A"; after T, "A 了". T can be any time, not necessarilly in the past but usually is, in which case you indeed can think of it as the "past tense", although we don't call it that way. -我们昨天看了一部电影。 (before a certain time yesterday, we didn't see the movie, then we did, 看了.) (when it's in the past and there's a specific time word like 昨天 in the sentence, v-了 usually means the action has completed. ) -昨天下雨了。 (it rained yesterday.) 了 is usually only descriptive. 过 is usually used in a certain context. when using 过, the verb must be repeatable. for example you can't say 我出生过. and verbs like 睡(sleep), 吃饭(have meal) are usually not used with 过, because 睡过, 吃过饭 are always true. another difference is that 了 is usually used with specific time words, like "yesterday", "last month". 过 is usually used with vague time words, like “before”, "a long time ago" and so on. hope it helps.

过 has to be tought of as : "have you ever done something", i.e. have you ever had the experience of.... Like, I suppose, Have you ever eaten fried crickets? 了 is more complicated. It has two main meanings and different positions in the sentence. Roughly, one way of using it is a "completed action marker" which does NOT correspond to a past tense (think: "when dinner is over, we will go out" = "having dined, we will go out", a completed action happening in the future), the other way of using it is as a "change of situation marker". ("Mother-in-law is coming" =she wasn't supposed to come, but she changed her mind). Thay are placed in a sentence in different ways according to meaning etc. Look here: This is very rough. There are many other meanings to 了. look here: http://comet.cls.yale.edu/mandarin/content/grammar.htm Regarding the past tense, that's all you'll find. In chinese, you use "time-framing" more than grammar, in order to express a past tense. You have to be more specific than you'd usually be in English. I advise you to note your own "time-framing" expressions as you find them. But you should also know that Chinese people would understand a lot out of context. If I ever put my "time-framing" notes all together in my PC, I'll send them to you.

了：1.表时态。表示动作或变化已经完成。 2.表语气。表示肯定或确定某种情况。 3.表示感叹。 过：1.经过。 2.度过。 3.过去。 4.通过。