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I am trying to learn/improve my English by remembering grammar rules. Every day, I read a lot of technical documentation and have many conversations with my colleagues from US.

I already have many phrase templates, but sometimes I urge myself to stop using this and try to figure out the rules by which a phrase was constructed.

So, how common is the usage of the sentence "I'm not understand". (Understand — is a verb in 1st form used after form of be.)

What rules were used? Why doesn't it sound like "I don't understand" or "I'm not understanding"?

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Where did you see "I'm not understand?" – gbutters Apr 18 '11 at 21:02
Best wishes learning English! There's also a community at http://ell.stackexchange.com/ that might be of interest to you in your endeavor. – WBT Jun 12 '15 at 14:41
up vote 7 down vote accepted

The phrase "I'm not understand" is constructed... well... badly. It's simply incorrect.

Your two alternatives are correct. You can use do understand or is understanding, but you can't use do understanding or is understand. You use do with the verb in base form, and is with the verb in present participle form.

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I just was confused by tons of google's result. Thanks. – bayda Apr 18 '11 at 21:09
For extra clarity: "I'm not understanding" would also be incorrect as a complete sentence to indicate that you don't understand something; normally you would always say "I don't understand". – Cerberus Apr 18 '11 at 22:16

"I'm not understand." is not proper usage. A native speaker would never say it.

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I just was confused by tons of google's result. Thanks. – bayda Apr 18 '11 at 21:10
Internet culture includes a tendency to deliberately mangle English grammar, as a form of wordplay. (The paragon exemplar of this is of course lolcat speech, e.g. "*I can has cheezburger?") – zwol Nov 12 '12 at 2:40

You are correct that "understand" is a verb, but you are using it as the sentence object, which must be a noun.

Use the noun "understanding" and it makes sense ("I am not understanding").

If you really want to use the verb "understand", use present perfect ("I do not understand")

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It must be an adjective or a noun. Remember that to be is a copula. – Matt E. Эллен May 3 '14 at 19:03

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