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I have a bad memory. is this right?

I have bad memory. is this right?

when can I use it as a countable vs. non-countable?
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This is right: I have a bad memory.

Use the uncountable form when you are speaking of the facility: Memory is a precarious reference.
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countable: I have fond memories of our ship-board romance. [Gosh, that was a long time ago!]