As I wandered the halls of two academic buildings today, I passed various classrooms with classes in session. No fewer than 3 times did I hear the phrase "That's a great question" uttered. I wonder how many times each day this phrase is used, and I wonder whether anyone says "That's a good question" any more. Good is not as good as great, so perhaps it is damaging to a student's self-esteem to label their question as merely good and not great. (?)
Other variants include: That's an excellent question. That's a really great question. That's an important question.
Is there an alternative? I'd rather not replace it with a more modern expression, e.g.: That's an awesome question. That question totally rocks. But is there anything as succinct yet effective?
That's a great question is distinct from I'm glad you asked that question, as the former in theory should mean what it says, but the latter can be used as a pedagogical technique for making a student feel better about asking a stupid question; i.e., the subtext is: Your question demonstrates a lack of understanding of the topic, but I'm going to use your question as an example of a common mistake that many students make and therefore you shouldn't feel bad about asking it because I can use it as a 'teachable moment' and therefore resolve what might be widespread confusion about this issue.
Earlier this semester, a student in one of my classes asked a question that indicated confusion about the topic of the day, and I said the typical professor I'm glad you asked that question thing and then did the teachable moment thing. Then I asked the class how they felt about a professor's saying I'm glad you asked that. Some students said they hated it because they know it really means That was a stupid question and you don't understand the topic, but they also admitted that they would rather a professor be kind that way than say directly what they thought of the question. They also don't like it when a professor tries too hard to find something positive about a totally wrong answer given by a student in class, even if the answer is totally wrong, as that can be confusing for everyone.
In a small or medium class, it is not so difficult to create an environment in which students feel comfortable asking questions. It is more difficult to do this in a large class, but it is certainly possible. That's a great question can be used to create just such a comfortable environment, but once it is clear to everyone that you welcome and enjoy answering questions in class (as I do), it can be tricky using the phrase. For example, what if you use it for some questions and not for others? Results of a brief informal and statistically invalid survey of a few students indicate to me that they notice things like this.
Thus far, I have been talking about the uttering of That's a great question by professors to students. I don't think this phrase does any harm, even if it is overused. However, there are circumstances in which it is not a great idea to use the great question phrase. In particular, people giving job talks during an interview might want to avoid this phrase. I have seen it annoy a number of colleagues to have a perky young interviewee tell them that they (a distinguished and brilliant person) asked a great question. Of course their question was great! Aside from the ego issues involved, it is particularly bad if That's a great question is used to mask the fact that the person hasn't thought about a particular issue and has no good (or great) answer.
9 months ago