There are other weaknesses. The easy verbal exchange of facts and ideas is unlikely to be the best way of learning practical activities or indeed any subject which, at the level of the class, is composed of uncontroversial facts. Few would find discussion a very helpful way of learning craft work, how to cook, or how to drive a car. There may be a place for a limited use of discussion to examine driving problems, but most of the learning is likely to be better achieved by other methods. Discussion is most appropriate to those subjects concerned with controversial issues about which there are different but equally tenable opinions. An acknowledged fact cannot be discussed as such, and at the levels normal in adult classes discussion attempted in the factual areas of mathematics and the sciences can be largely a waste of time. Students indeed may assert that discussion methods have failed to achieve anything, even in classes concerned with controversial subject matter. Although this is usually a faulty subjective impression, it is worth noting that sometimes in a well-established class the students have already contributed so much of their knowledge and views that nothing new is being added. Like all of methods, discussion has to be used with discretion, after an assessment of all the circumstances.