The is the sentence I'm uncertain about:

These old journals are wonderful to learn what life was like a century ago.
I know the infinitive is 'to learn.' I think it is being used as an adverb. It's modifying the adjective 'wonderful.' It's not a noun used as a direct object or a noun as a subject. Could it be an adjective because it's modifying journals? These types of sentences confuse me. I'd be grateful for any help, thank you.

5 answers

That's a bad sentence. Are journals able "to learn" anything?

Better sentence: These old journals are wonderful for us to read and learn what life was like a century ago.

If you were given that badly phrased sentence in a text or by your teacher, you need to ask for better educational resources.
Yes, the sentences we receive are really bad! I've talked to this teacher about this. You know how there are some who feel they are above question? She's one of them. With that in mind, do you concur it's an adverb clause? Thanks so much!
Yes, you're stuck with this!

Yes, "to learn" is an infinitive, being used here as an adverb modifying "wonderful."
Thank you Writeacher, I pray you are blessed for your help.
You're welcome ... and thank you, too!