a form of

0Hi,02br
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00I think with the phrases like 'a kind of' or 'a sort of', what comes after need not have an article like here:02br
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01i00a kind of mental illness02i02br
02br
01i00a sort of mental illness02i02br
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00My dictionary seems to say 'illness' is countable and thus, I think you can say 'an illness' or 'three illnesses'. Would I be able to put any adjective between, except those that indicate numbers between 'a' and the above words 'kind' and 'sort' and maintain the article-freeness?02br
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01i00a 01u00situation-changing02u00 kind of mental illness 02i02br
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00Then I am confused about the phrase 'a form of'. Are the sentences with the phrase need not concern with an article like the ones above?02br
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01i00a new form of 01u00mental illness02u02i02br
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01i00a normal form of 01u00Christian practice02u02i0-