I did read everything above before asking my question. I'm not concerned about losing a heart, but want to understand why 'Those books are popular.' is acceptable and 'These books are popular.' is not acceptable. I don't see a difference in 'these books = ces livres' and 'those books = ces livres' when I look at your earlier comment. I am not ignoring the second half of your comment, but looking at the sentence as it was presented, "Ces livres sont populaires," I don't understand why 'those' is acceptable and not 'these.'
These books = ces livres / ces livres-ci
Those books - ces livres /ces livres-là
Thanks for any help you can provide.
I checked again in the program and I confirm that "these books are popular" and "those are popular" are accepted, so I assume the issue was in the construction of your sentence, not on the alternative demonstratives:
Strictly speaking, "these are popular books" should back translate to "ceux-ci sont des livres populaires" (there are other lessons on demonstrative pronouns later, using this format).
The meaning is not very different, but there was no need to change the structure of the sentence.
Disclaimer - I'm not a native speaker. "Ce" is singular, but can be used to replace "ils/elles sont" in a sentence (meaning "they" in English) and therefor be considered plural. For example: "Ils sont mes amis" - "Ce sont mes amis" - "They are my friends". "Ces" is always plural and would be "these/those" in English. For example: "Ces stylos sont bleus" - "These pens are blue". Hope that helps, and any native speakers please feel free to comment/correct!
In the expressions "c'est" or "ce sont", "ce" is a pronoun and acts as the subject of verb être.
On the other hand, "ce/cet, cette, ces" are demonstrative adjectives followed by nouns, which they agree with.
Note here that the difference "ce/cet" is about the following noun (or adjective) starting with a consonant or a vowel/non aspired "h". - ce train - cet ami - cet horrible jour - cette fille - ces enfants
When you're learning a second language, you learn to be more precise in thinking about language in general. You start noticing things like this:
"These books are popular." is not the same as "These are popular books".
Ces libres sont populaires is not the same as Ceux-ci sont des livres populaires.