Aristotle is as wise as it gets. So when he opened his mouth, we better listen. Unless of course you have an uneducated mind. Many times I am amazed when talking or debating with someone I believe is educated, and they have no capacity to entertain a different opinion. When I say educated, I do not necessarily mean someone with a diploma or degree. But rather someone that has been around the block, someone with some knowledge, someone with a keen interest to learn or listen, someone who has some logical reasoning capacity.
Most of us have fairly strong ideas, believe in certain things and think we can distinguish between right and wrong. But how do we handle facts, opinions or ideas that contradict what we believe in? Do we raise a mental block and stop listening? Do we get angry and turn away? Or do we listen, trying to grasp what the other person is saying? Do we at least try to understand the opposing point of view? Many people just shut down, refusing to entertain the idea, to learn from it.
Wisdom teaches us to entertain any new idea, even though we may not agree with it or accept it. Next time you are fortunate to be in the company of a person who thinks differently, that comes from a different planet (Mars or Venus for instance), that has a different culture, a different upbringing and a different frame of reference shut your mouth and open your ears and mind. Aristotle did not say you have to agree with diferent thinking or accept different values. He merely said you need to entertain it.
It may be helpful to consider whether entertaining a thought is the same as being open-minded. It may be that they are more-or-less equivalent in the sense that they both imply consideration (of a proposition, idea, etc.), although entertaining a thought is more of an active process whereas open-mindedness seems to be more passive. The former, in the context of Aristotle’s quote, seems to entail adopting a thought in order to better test for truth or falsehood, whereas open-mindedness connotes a more general receptivity toward, or maybe respect for, the thought.