"It is impossible to think about that."
Translation:Il est impossible de penser à cela.
I think the reason is that cela and ceci is specifically used to refer to something indefinite or to refer back to something previously mentioned
why do some of the constructs require 'de' or 'a' before the second verb form? how does one know when to use one or the other?
I've tried to find a good answer for you, but mostly you just have to learn which phrases are followed by "a" and which are followed by "de" https://www.frenchtoday.com/blog/french-verb-conjugation/why-french-verbs-followed-preposition-a-infinitive
Aside from the strange thing that French sometimes requires 'de' or 'à' after a verb, there is the fact that you want to include the entire phrase "penser à cela". So, using 'de' leads into the phrase.
I thought of Ce n'est pas possible de penser à ça. I wonder if it's accepted.
"Il est impossible de penser a propos de cela." Any reason why this was unacceptable (ignore diacriticals, please) given how the word hints read?
Which is why I said "ignore diacriticals, please" since DL warns but generally does not reject on that basis.
Tom, sometimes it does reject on that basis - notably when leaving out the diacritical changes the meaning of the word as is the case here.
Hi LisaLisko, 'il est impossible de + infinitive' - after BE + impossible, 'de' must follow. Sometimes we just have to accept that another language does it differently from our own.