If You Can't Say it You Don't Understand it

In my MCCC Philosophy of religion classes I give the students three one-one-one, 10 minute oral exams. They know in advance the questions I'm going to ask them (such as, "Explain Anselm's Ontological Argument for the Existence of God"). 

On occasion a student complains (even though they have been instructed) about the oral exams. They say, "I understand the material. I just can't say it." (Which means: They don't understand the material.) 

Or, a student says: "I can't say the answer, but I can write it down." (Which means: they don't understand the material. This may not be true in everything, but it's true in philosophy. Or, in medicine. Imagine a doctor who tells you, "I can't say what's wrong with you, but I understand it and can write it down on paper." Avoid doctors like this.) 

I evaluate the students' understanding of the material, not their agreement or disagreement with it. They cannot begin to evaluate arguments they don't understand.

Plus, giving oral exams protects me from this.