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I know this sentence is correct:

This problem has been studied by Dave

Is it also correct to say?

This problem has studied by Dave

If not , why? From my previous knowledge, I guess we have to write "Dave has studied this problem". I might be wrong but that's why I'm confused.

If it is correct, what are the differences between the above sentence with this :

This problem is studied by Dave

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"This has studied by Dave." is not correct but
"Dave has studied this." is correct.

I believe you have simply mixed up your conjugations after learning the passive voice.

"Has studied" is the Present Active 3rd person singular form of the verb "to study". In your sentence, you are using an active verb in a passive sentence which is not allowed.

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  • I almost knew that has studied by Dave is not correct, but I'm confused if "has studied by Dave" is incorrect why is "has been studied by Dave" is correct? I assumed they are similar but "has been" continue a situation to the present. Am I wrong? Is "has been" passive?
    – MFR
    Oct 10, 2016 at 2:43
  • Yes, has been studied is a passive verb construction.
    – Alan Carmack
    Oct 10, 2016 at 2:48
  • In English, sentences can either be expressed in the "Active voice" or the "Passive voice". In an Active sentence, the subject performs action on the object. For example:**Dave studies Math" is an active sentence because Dave (the subject) is performing the action (studies) on the object (Math). In a Passive sentence, the subject has an action performed on it by an agent (marked with "by"). For example:**Math is studied by Dave** is a passive sentence because Math (the subject) is having the action (is studied) performed on it by Dave (the agent). to be continued...
    – G-Cam
    Oct 10, 2016 at 2:50
  • English verbs conjugate differently depending on whether the sentence is active or passive. Passive constructions are characterized by a form of the verb "to be". "Has been studied is the Present Perfect Passive form of to study. Has studied is the Present Perfect Active form of to study.
    – G-Cam
    Oct 10, 2016 at 2:52
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    @Zakiya Honestly, I'm not certain "has been being studied" is grammatical (I'm also not certain that it is not grammatical). If it is in fact correct, it would mean that the studying began in the past and continues to the present moment (implying that it is still continuing). This meaning would much more likely be expressed using the active voice with a generic subject: "They've been studying it for years." or with a compound sentence: "It's been studied for years and continues (to be studied) to this day."
    – G-Cam
    Jan 22, 2017 at 5:13

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