When something is not worth praising, you should give (an) honest criticism about it.
Would you add ”an”?
I would say: When something is not worth praising, you should give an honest criticism of it. content=a+criticism+of%2C+a+criticism+about&year_start=1800&year_end=2000&corpus=15&smoothing=3
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I would say:
When something is not worth praising, you should give an honest criticism of it.
https://books.google.com/ngrams/graph?content=a+criticism+of%2C+a+criticism+about&year_start=1