Final answer:
The principle of autonomy reflects the idea of treating a subject as an autonomous agent, allowing them to make decisions about their own healthcare or participation in research trials.
Step-by-step explanation:
The ethical principle that reflects the idea of treating a subject as an autonomous agent is the principle of autonomy. This principle states that individuals have the right to exercise agency and make decisions about their own healthcare or participation in research trials. Autonomy is protected through informed consent, which ensures that individuals have all the relevant information to make an informed decision. The principle of autonomy also emphasizes the importance of respecting the rights and choices of trial participants.