A tentative explanation to a question about the natural world is a

law

hypothesis

theory

fact

Hypothesis

Fact: Something that is always the case (ex: The plant has grown)

Hypothesis: Something that is based upon some evidence (If the plants grows in sunlight, then that's the only thing it needs to survive

Law: Something that explains why something happened (The plant grew while in sunlight, so it needs the sun to survive)

Theory: A hypothesis that has been proven through evidence (When I only fed the plant fertilizer, it didn't grow, but when I fed it fertilizer and gave it sunlight, the plant blossomed more and more)