It's a bit tricky because "learned" can also be the past participle of the verb "to learn." Here's how to tell the difference:
* Adjective: "Learned" describes a noun. For example: "He is a learned man." (meaning he has much knowledge)
* Past participle: "Learned" acts as part of a verb phrase. For example: "I have learned a lot."
So, the context determines whether "learned" is an adjective or a past participle.