The sentence that text is in doesn't make sense. It looks like an editing error to me.

Student or Learner
What does "the messages are only silly and trivial to be entirely unjustified by his experience" mean?
It is interesting to note that du Prel proclaims the assertion that the messages are only silly and trivial to be entirely unjustified by his experience, while at the same time he asserts that he has found no traces of superhuman intelligence, but of course, before pronouncing upon such a point, one has to determine how a superhuman intelligence could be distinguished and how far it would be intelligible to our brains.
"The History of Spiritualism," by Arthur Conan Doyle
Last edited by jacob123; 20-Sep-2020 at 21:43. Reason: it was uncomplete (OP); Spread text across whole box (emsr2d2)
The sentence that text is in doesn't make sense. It looks like an editing error to me.
I am not a teacher.
Last edited by jacob123; 20-Sep-2020 at 22:03. Reason: it was wrong.
I am not a teacher.
Please correct the information in your member profile. You appear to have chosen three random responses.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
It looks as if Conan Doyle just lost track of what he was trying to say in such a ponderous sentence.
If you substitute "is" for "to be" then the whole thing starts to make some sort of sense.
Retired magazine editor and native British English speaker - not a teacher
It makes good sense to me: Someone asserted that the messages are silly and trivial. Du Prel disagrees with this, based on his experience.
I can understand why other members are having difficulty. The sentence uses the pattern: proclaim something to be something
Du Prel proclaims the assertion that the messages are only silly and trivial to be entirely unjustified by his experience
Jacob, I see you are also posting threads about this book on WordReference Forums.
Please do not post the same question on both forums at the same time.