了 vs 过 - Completed vs Experience

Both 了 and 过 are particles. They do not have a meaning on their own. They attach to verbs to give them 'aspect.' Aspect is just a fancy word for 'how the action flows through time.' In English, we change the verb itself (eat vs. ate). In Chinese, the verb stays the same. We just add a little tag after it. If you say 吃 (chī), it just means 'eat.' Add 了, and it is 'eaten.' Add 过, and it is 'have eaten before.' It is like adding a sticker to a box. The box is the verb. The sticker tells you if the box is full or if you have owned that box before.

1. 1For completion: Verb + 了. Example: 我买了书 (I bought the book).
2. 2For experience: Verb + 过. Example: 我买过书 (I have bought books before).
3. 3To negate completion: 没 + Verb (Drop the 了). Example: 我没买书 (I didn't buy the book).
4. 4To negate experience: 没 + Verb + 过. Example: 我没买过书 (I have never bought books).
5. 5For questions: Verb + 了 + 没有? or Verb + 过 + 吗?

Use 了 when the focus is on the result. You finished your homework. You arrived at the party. You bought the groceries. It is about the specific event. Imagine you are at a restaurant. The waiter asks if you want more water. You say 我喝了 (I drank [it]). You are done.

Use 过 when you want to talk about your life resume. Have you ever been to Paris? Have you ever tried stinky tofu? Have you ever loved and lost? It is about the 'ever.' If you are in a job interview, use 过. 'I have used this software before' is 我用过这个软件. It shows you have the skill. It is not about one specific time you used it this morning. It is about your total experience.

Do not use 了 for things you do every day. If you run every morning, do not say 我跑了步. That sounds like you just finished a specific run. For habits, just use the verb.

Do not use 过 for things that are happening right now. You cannot say 我正吃过饭. That is like saying 'I am currently having had a meal.' It hurts the brain.

Also, do not use 过 for things that have no lasting 'experience' value. You usually do not say 我开过门 (I have opened a door before) unless it was a very special, magical door. It sounds too dramatic for daily chores. Think of 过 as the 'Storyteller' particle. If there is no story, stick to 了.

A big mistake is using 了 with 没. You should say 我没去 (I didn't go). Never say 我没去了. This is a grammar traffic light. 没 and 了 usually do not hang out together in the same lane.

Another mistake is using 过 for things that just happened. If you just finished your coffee, say 我喝了咖啡. If you say 我喝过咖啡, your friend might think you are talking about a coffee tasting event you went to three years ago.

Finally, don't forget the 'Change of State' 了. If you say 下雨了, it means 'It is raining now' (it wasn't before). 过 cannot do this. 下过雨 means 'It rained before' (but it is dry now).

Let's look at 去 (to go).

我去了 (I went/I'm gone): I am likely at the destination or on my way. The action is complete.

我过去 (I go over): This is a direction, not an experience! Be careful.

我去过 (I have been): I went there in the past, but I am back now.

Think of 了 as a movie scene that just ended. Think of 过 as a movie you saw a long time ago. If you are still in the cinema, use 了. If you are at home talking about the movie, use 过.