How can I express "a particular/a certain" thing?

Question

I am studying vocabulary and I came across the word 然る, either read as さる or しかる (usually written in Kana) and means "A Particular/A Certain" noun. However, there was only one example sentence on there and it wasn't marked as a Common Word, which seems to be a red flag for me in terms of learning the correct vocabulary.

How can I use さる／しかる to express "a particular/a certain" thing? Secondly, is there a better or more natural way to express this phrase?

Example idea:

卒業するように、さる授業を取らなければいけません。
In order to graduate, you must take a certain class.

Answer 1

It's always read as さる when it means "a certain ～". You can think of it basically as a literary version of ある meaning "a certain ～" or "one ～". In relatively casual situations, さる sounds more or less "serious", and it sometimes has a nuance of "don't pry into this".

• ある授業を取らないといけません → sounds natural and neutral
• さる授業を取らないといけません → uncommon; may sound like this class is somehow special/problematic when used in a casual blog article or such
• ある会社 → neutral
• さる会社 → maybe the speaker does not want to disclose the name of the company