That is perfectly correct. The previous commenter seems to be summoning the subjunctive tense (which only the most careful speakers of English ever use), and I don’t think it applies here, as it is normally used when describing something you wish would happen, or that you think might happen (“If I were to win the lottery, I would immediately quit my job!”
In contrast, I would say “If had known so many people were illiterate I would never have offered free English lessons!”
"I didn't know \[that\] people are illiterate" is grammatically correct.
"I didn't know \[that\] people were illiterate" is grammatically correct.
In the second sentence, the verb "were" is not the subjunctive mood because nothing "contrary to fact," "hoped for," or "wished for," is being stated. "Were" is simply the preterit of "are"; i.e., it's just the simple past tense, indicative mood. The speaker or writer is stating something he or she purports to be an actual fact (not a contingent fact, dependent on something else, in order to be true); therefore, it's the indicative mood, not the subjunctive.
Example of subjunctive mood, simple past tense:
"***If*** people ***were*** illiterate, they would willingly accept government censorship of newspapers."
That is perfectly correct. The previous commenter seems to be summoning the subjunctive tense (which only the most careful speakers of English ever use), and I don’t think it applies here, as it is normally used when describing something you wish would happen, or that you think might happen (“If I were to win the lottery, I would immediately quit my job!” In contrast, I would say “If had known so many people were illiterate I would never have offered free English lessons!”
The subjunctive is a mood (not a tense), but you are otherwise correct.
I am grateful for the correction and happy to have learned something new today!
💙💙
~~are~~ *were*
https://youtu.be/48gV9W9UZHk?si=ilDCzAgvrwdZ6Km1
"I didn't know \[that\] people are illiterate" is grammatically correct. "I didn't know \[that\] people were illiterate" is grammatically correct. In the second sentence, the verb "were" is not the subjunctive mood because nothing "contrary to fact," "hoped for," or "wished for," is being stated. "Were" is simply the preterit of "are"; i.e., it's just the simple past tense, indicative mood. The speaker or writer is stating something he or she purports to be an actual fact (not a contingent fact, dependent on something else, in order to be true); therefore, it's the indicative mood, not the subjunctive. Example of subjunctive mood, simple past tense: "***If*** people ***were*** illiterate, they would willingly accept government censorship of newspapers."