Let's fix the sentence, then fix the "rule." Original: A well-known medical specialist stated that it (is/was) physicians' moral duty to inform patients about the possible side effects of any drugs they (will/would) recommend. Corrected version: A well-known medical specialist HAS STATED that it IS A physician'S moral duty to inform patients about the possible side effects of any drugs (THAT) THE PHYSICIAN recommendS. Analysis: 1 - / A well-known medical specialist HAS STATED / 2 - / that it IS A physician'S moral duty / 3 - / to inform patients about the possible side effects of any drugs / 4 - / (THAT) THE PHYSICIAN recommendS. / 1 - /A well-known medical specialist HAS STATED / Use "has stated," if the action occurred during an unfinished time period. Example: "... has stated today," "... has stated this week," "has stated recently," or "has stated" (recently assumed). Use "stated," if the action occured during a finished time period. Examples: "... stated yesterday," "... stated last week," "... stated on March 1, 2002." More information about the simple past and present perfect here: https://www.ef.com/ca/english-resources/english-grammar/present-perfect-vs-simple-past/ 2 - / that it IS A physician'S moral duty / Use "a physician's moral duty" to indicate a moral duty for all physicians. Use the simple present "is" because the moral obligation is a general truth. More information about the simple present: https://www.ef.com/ca/english-resources/english-grammar/simple-present-tense/ 3 - no analysis 4 - / (THAT) THE PHYSICIAN recommendS. / Replace "they" by "the physician" for clarity. Use the simple present "recommends" because recommending medicine is a repeated action. More information about the simple present: https://www.ef.com/ca/english-resources/english-grammar/simple-present-tense/ As for the "rule," that's a big discussion. I'll add a brief comment.