Chinese has no tense. It has aspect, carried by a small set of particles, and the difference is the source of more learner error than everything else in the grammar combined. The particle le is not a past tense marker, and treating it as one produces sentences that are wrong in a way no English speaker's instinct will flag.
Nothing changes shape in this language: no conjugation, no plurals, no agreement. All of the information that would have gone into an ending has gone into two places instead, which are the order of the words and about a dozen particles.
Six patterns and the grammar is most of the way there
- 我吃饭, I eat rice. Subject, verb, object, with nothing marked on any of the three.
- 了 marks completion, not past tense, which is the distinction that takes longest. It says an action is finished or a situation has changed, and it can appear in a sentence about the future.
- 一本书, one book, and the middle character is a measure word. Chinese requires one between a number and a noun, and which one depends on the shape and kind of the thing counted.
- 的 links a modifier to a noun, doing the work of English possessive and relative clauses alike: 我的书 is my book and 我买的书 is the book I bought.
- 吗 makes a question when added to the end of a statement, leaving the word order untouched.
- 把 moves the object forward, before the verb, to say what was done to it. It is the one construction that genuinely rearranges a sentence and it is common in speech.
Two les, in two positions, doing two jobs
One le sits immediately after the verb and marks that the action was completed. The other sits at the end of the sentence and marks a change of state, that something is now the case which was not before. They look identical, they are written identically, and they mean different things, and a sentence can contain both.
The reason this matters more than a normal grammar point is the false friend inside it. A completed action is usually in the past, so the first le appears in a great many past sentences, and a learner concludes it is the past marker. Then they attach it to habitual past actions, to states, and to negatives, where it does not belong, and each of those is a sentence a Chinese speaker will understand and immediately notice.
The other two aspect particles are cleaner. Guo marks that something has been experienced at some point, which is closer to the English present perfect than anything else here. Zhe marks that a state is ongoing. Neither says when, and none of the three is a tense: when is carried by a time word at the front of the sentence, and once it is there nothing else in the sentence marks time at all.
Filing le under past tense, and never getting it back
Here is where the grammar stalls, and it is a mapping error rather than a gap. The rule that gets absorbed in the first month is le equals past, and it is right often enough to survive contact with a lot of material. Every sentence it produces correctly reinforces it, and the sentences it produces incorrectly are understood, so nothing pushes back.
Three tests break it and they are worth doing in one sitting. Say something habitual in the past, such as that you used to walk to school: no le. Say something in the past that is a state rather than an event, such as that the room was small: no le. Say something did not happen: the negative takes a different marker and le disappears. A learner who has produced those three correctly has replaced the wrong rule with a usable one, and it takes an afternoon rather than a term. Getting somebody to catch the ones that come out wrong is what a paid hour is for, in what a teacher is worth, and what you can do alone.
Where each piece goes
The order, which is doing the work the endings would have done
Nothing changes shape in this language, so the position is the grammar and it is stricter than in a language with cases.
- The topicWhat the sentence is about, which English often puts last
- WhenA time word, and once it is here nothing else marks time
- WherePlace before manner, and both before the verb
- HowManner, and anything qualifying the action
- The verb, with its particleAnd le immediately after it, if the action completed
- The objectLast, unless it has been moved forward on purpose
The last step carries the exception. There is a construction that pulls the object in front of the verb, and it is used when something is being done to the object rather than merely with it, which is the one place this order genuinely bends.
Two references written for this problem
The Chinese Grammar Wiki is free, it is organised by level, and its entries are built around exactly this kind of confusion: separate pages for the two les, with contrasting example sentences rather than a rule. It replaced the grammar appendix at the back of a textbook, which states the rule correctly in three lines and gives you nothing to compare against.
Tatoeba is the second, a free collection of sentences translated by volunteers into many languages, searchable. It replaced inventing your own example sentences and having no way to check them, which is the position most self-taught learners are in. Search a particle and read thirty real sentences containing it: the pattern is visible in the data before it can be stated, which is the same reason a corpus beats an explanation everywhere in this pillar.
The mistake: leaving out the measure word
You cannot put a number directly in front of a noun. Between them goes a classifier, chosen according to the noun, and there are dozens of them, some obviously motivated by shape or category and some purely conventional. Leaving it out is the most audible beginner error in Chinese and it happens in the most ordinary sentences, because counting things is ordinary.
The fix is a storage decision rather than a grammar exercise. Every countable noun goes into your notes with its classifier attached, from the first day, in the same way a German noun takes its article. There is a general purpose classifier that will carry you through a conversation when the right one will not come, and using it everywhere is a recognisable learner accent rather than an error. Both of those are true at once, and the second is what makes the first survivable.
What the word order carries instead
Because nothing agrees and nothing conjugates, position is doing the work, and the order is stricter than in a language with endings: time before place, place before manner, and all of them before the verb. The topic comes first and the comment follows it, which is why a Chinese sentence often begins with something an English sentence would put at the end. The particles that carry the aspect are unstressed and short, so hearing them at speed is a separate problem, in hearing tone at conversational speed. The words being ordered are mostly two characters each and largely transparent, in two character words, and guessing the meaning of a new one. And every one of those characters carries a tone that the grammar will not help you recover, in four of them, and what happens when you get one wrong.