If a belief is justified, there is something that justifies it, which can be called its "justifier".
The thing that justifies a belief can be called its "justifier". If a belief is justified, there is something that justifies it.
If a belief is justified, there is something that justifies it. The thing that justifies a belief can be called its "justifier".
If a belief is justified, there is something that justifies it. The thing that justifies a belief can be called its "justifier".