Cambridge Dictionary has a definition of ‘certain’ as a determiner.
certain
determiner
uk /ˈsɜː.tən/ us /ˈsɝː.tən/
B1
particular but not named or described:
However, neither in the Wikipedia article nor in other sources, it is possible to find exactly what type of determiners this word belongs to and what is the function of this type of determiners.
Let’s look at the first example from the same dictionary entry:
We have certain reasons for our decision, which have to remain confidential.
Why the determiner was used, as well as the meaning of the word ‘certain’ is completely unclear. It can be removed, and the meaning will not change.
We have reasons for our decision, which have to remain confidential.
Let’s look at an example from the page 309 of the book An Institutional Approach to the Responsibility to Protect, Gentian Zyberi, Kevin T. Mason, Cambridge University Press, June 27, 2013
Also the General Assembly carries certain responsibility for maintaining international peace and security, especially when the Security Council is deadlocked.
Nothing will change in meaning if you just say:
Also the General Assembly carries responsibility for maintaining international peace and security, especially when the Security Council is deadlocked.
Why do we need this determiner if it doesn’t really mean anything?