"I didn't buy that" without 了

Question

Is 了 ever/sometimes/never omitted for past subjunctive? What if not subjunctive; i.e., positively something did happen.

wohok.com gives for 没 two example sentences

我没买这个
我没有买这个

and translates both as "I didn't buy this." (Could argue this is not subjunctive, but I am familiar with languages where a negative is always subjunctive.

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Aside …

What is the difference between 没有+V. and 没+V.? answers that there is no practical difference between 没有 and 没, but a comment suggests subtle differences in meaning or connotation. (Have to translate a lot of Chinese to figure out what it is saying!)

Answer 1

了 never appears in past negation.

By definition, one of 了 grammatical functions is to indicate completed action, and not past tense. Hence, if the action did not happen at all (没), it has also never been completed.

他还没来 - He still didn't come (and not他还没来了）

A side note to that is that 了 would appear in present negation.

他不来了 - He is not coming.

Answer 2

regarding 了 and negation note e.g. http://human.bsru.ac.th/e-learning/@PWP%20to%20PDF/57%20PDF%20Chiness/57%20Chiness%20Nongnut%202104308.pdf

3）否定句中

♥ 否定句中，“没”与“了”不能同时出现。

♥ 我吃完饭了。→我没吃完饭。→*我没吃完饭了。

♥ 注意：动词前有表示一段时间的词语，句末可用语 气助词“了”。

♥ 我好长时间没看到他了。

♥ 他好久没上班了。

♥ 一年多没回家乡了。

naturally still applies to conditional clauses corresponding to English past subjunctive mood 过去虚拟语气:if I had not bought that 要是我没（有）买这个 (w/o 了） naturally 过 is possible (要是)我没（有）买过这个

to find more articles concerning absence of 了 in negative clauses search web using e.g. 汉语语法：动态助词＂了＂ 用法与意义＋否定句，get e.g. http://www.cim.chinesecio.com/hbcms/f/article/info?id=3c85e3090860428da0854f5fbab24aa5 : (三)否定句和疑问句

1.带有表示完成的“了”的句子的否定形式是没(有)+ 谓语动词注意：在用“没”的句子里,不可以再出现“了”。

2.问句比较容易,用“吗”的疑问句和正反疑问句。如：他写了三个汉字吗？

他写没写三个汉字？

for English could google "Chinese grammar: aspect particle 了: negation" get e.g. http://intensive-chinese.blogspot.com/2012/01/used-as-aspect-particle-and-as-modal.html (f) If you want turn an affirmative sentence which contains the aspect particle “了” into a negative sentence, you can do so by prefixing the adverb “没有” to the verb whilst dropping the aspect particle, e.g.: 他 吃了 晚饭 就 去 看 电影。 他 没有 吃 晚饭 就 去 看 电影。

We should never use “不” to negate a verb in the past tense or present perfect tense. For this purpose, we use “没有”; and when using “没有” , we also drop “了” .