Simplify for Clarity
Let's strip this sentence down:
Skeptical of the abilities of prophets to tell the future, a significant number of philosophers in Athens began to value reason over revealed truths.
The first clause adds meaning, but isn't essential to the core sentence.
A significant number of philosophers in Athens began to value reason over revealed truths.
The last clause only tells us a bit more about how much they're valuing reason, so it's not essential.
A significant number of philosophers in Athens began to value reason.
Significant is just an adjective, let's drop that.
A number of philosophers in Athens began to value reason.
Who cares where these philosophers are located?
A number of philosophers began to value reason.
"Of philosophers" is just a prepositional phrase describing what we have a number of.
A number began to value reason.
This is a perfectly valid sentence. "A number" is the subject. This is one of the most common usages of the word 'number'.
Dictionary Definitions
Some different phrasings of its definition from a few dictionaries:
Wiktionary:
- Quantity
Reference.com:
- the sum, total, count, or aggregate of a collection of units, or the like
Merriam-Webster:
1a. (1) : a sum of units : total (2) : complement 1b (3) : an indefinite usually large total (4) plural : a numerous group : many (5) : a numerical preponderance
Therefore, here are some other, mostly synonymous phrasings:
Many (philosophers) began to value reason.
A group (of philosophers) began to value reason.
A preponderance (of philosophers) began to value reason.
A Skeptical Number
So the subject of the sentence being modified is not "philosophers", it's "a number". It might be more useful to look at it as "a number of philosophers", but the phrase specifying what we have a number of may not always be present in the sentence. It could be from context:
At this time there were a great many philosophers in Athens. Skeptical of the abilities of prophets to tell the future, a significant number began to value reason over revealed truths.
So yes, 'skeptical' can modify number, because "a number" is a group of things, and the things in the group can be skeptical.