Be very, very careful what you put into that head,
because you will never, ever get it out.

Thomas Cardinal Wolsey (1471-1530)
Teaching FAQ
Click on the symbol for its explanation.

This FAQ (Frequently Asked Questions) is written by Alistair B. Fraser. It is in response to questions posed over the years by readers of the  Bad Meteorology  pages. If you have arived on this page without having read those pages or the other  Bad Science  pages, then what follows, will probably make little sense.

Although the questions presented here are often ones asked by a specific person, each is chosen to characterize a group of similar questions which have been asked about the topic.
Issues discussed below

Employment of metaphors
Persistence of textbook errors
Teacher intransigence

General questions about teaching:

Employment of metaphors
I realize you may be more sensitive than I am to the error of “the water holding capacity” of the atmosphere, but I must point out that until you attracted my attention to it, it never really bothered me. I have always known that cloud formation was a matter of equilibrium between condensation and evaporation/sublimation, but I have always considered the image of the “water holding capacity” as being no more than an metaphor, like that of the sun rising in the east or crossing the ecliptic on September 21st.

Metaphors provide a teacher with a powerful means of building bridges between old ideas and new ones. However, they also open up pedagogical problems: teachers recognize them as metaphors, but virtually all students take them as literals.

Indeed, consider the specific case you raise, that of the water behaving the way it does because of a holding capacity of air. Treated as metaphor or simile it has some merit: water behaves approximately as if its condensation and evaporation were determined by a temperature-dependent holding power of the air. The phrase, behaves approximately as if, is soon lost with the result that students, teachers and textbook writers soon believe that air actually has a temperature-dependent holding power. The next step is that they attempt to offer an explanation of that which is nonsense: there are many books out there which have transformed the metaphor into a literal and then proceed to explain just how it is that air can do this holding (discussions of how the space between molecules varies with temperature), and they are all junk.

This is why my pages are not directed to scientists, who can be given the benefit of the doubt in the employment of metaphors among themselves. Rather they are directed towards teachers, who must deal with students who inevitably take a metaphor as a literal with the result that they believe in processes which do not accord with nature.

There is another issue that should be raised in deciding whether to accept the pedagogical use of a metaphor: is the result markedly simpler. I would argue that in the case you raise, the explanation involving a mystical holding power of the air does not make the explanation any simpler than one which allows for molecules arriving and leaving the liquid or vapor. So, why employ a metaphor which is both misleading and no simpler than the correct explanation?

Persistence of textbook errors
I teach Honors Biology to 9th grade students at.... Last year when I was surfing the web I came across your  Bad Science  web site and was so glad you have addressed these issues. It’s about time! SOOO last year I began spreading the word about the Greenhouse effect while teaching the CO2 - O2 cycle. Last year, as well as this year, the new revised concept was greeted with much skepticism, especially when the science book as well as many others, and even many web sites use that awful term TRAPPED. The biggest question that the children always ask is why does the book say this??? Why are textbook authors perpetuating this misinformation? I do the best I can to explain. Can you help?

Well, now you have wandered into an area of my incompetence: the behavior of people. Anything I can offer is by way of speculation only.

Probably the simple answer is that the textbook writers are like the rest of us, they largely just parrot what they have been taught rather than critically examining every idea. Most of us are inclined to accept something without question merely because it has been presented by a supposed authority.

Will and Ariel Durant once wrote a book (the last of their many history books) entitled, The Lessons of History  (1968, ISBN: 0671413333). In it, as I recall, they claimed that there had not been a single silly idea which had ever died out. They just kept being repeated and always found acceptance among the uncritical (the incredible is fodder for the credulous). Whether their statement can be accepted as an absolute or not, I cannot say, but there are plenty of examples which support their position. One will do: astrology.

But, in suggesting the above, I have merely pushed the question back a few levels: why were those writers taught the nonsense, and so on back to the originator of the idea. Usually there is a good historical reason. The idea of air having a holding power for water vapor dates to the eighteenth century and was a reasonable speculation at the time. It was shown to be false early in the nineteenth century, but it is still taught as fact nearly two hundred years later. Even astrology was a plausible guess two to three thousand years ago.

The problem with the use of TRAPPING, however, probably stems from a misunderstanding of the behavior of budgets. The maximum value of your bank account (or the minimum value) does not occur because money is being trapped, but because it is not being trapped. If there is more money coming into your account than leaving it, the total will rise. But, the maximum (and minimum) value occurs when there is a balance between that which is coming in and going out. So, if your bank account is sustained at a uniformly high level (c.f., the greenhouse effect), then there is no trapping.

Mind you, there are historical accidents at work here also. The name, greenhouse effect, is a misnomer based upon a mistaken idea of how the greenhouse works. It is a misconception which was pointed out nearly a century ago. That, of course, has not stopped it from being taught. Sigh....

So, how do you explain this to your students. I don’t really know. I tell mine the same thing I told my children: sometimes you can learn because of the teacher; sometimes you learn despite the teacher; but, learn you must, in either case. Substitute the word, book, for teacher and it would seem to cover the situation. In the end, it is actually the student’s responsibility to himself (herself) that requires the learning, not the book, the teacher, or the parents. An awesome responsibility, but one which students in grade nine are probably prepared to face.

Teacher intransigence
I am a high school student that has repeatedly confronted my teachers with examples of “bad education” and find that they become irritated. One of my science teachers went so far as to tell me that we got dizzy because our brain banged around inside our skulls. I do, however, continue to correct them.

You are in a difficult position which requires a bit of tact. While I clearly don’t condone the teaching of nonsense, I am also sympathetic to the teacher who, thinking he or she is doing the right thing, gets upbraided by a student for errors. By all means bring these issues to the attention of your teachers, but do so in a way which does not embarrass them in front of others. This is not only the courteous thing to do under all circumstances, it is far more likely to be effective and work to your benefit.

Recall that the object of the game is for the teachers (and students) to get it right. Sometimes this is best accomplished by a gracious observation rather than a confrontation. You are trying to make sure that the teaching is good, rather than score points with your fellow students.

Nevertheless, having encouraged you to be gracious, I must admit that I have little tolerance for teachers who cover up their own failings by throwing names or criticisms at their students. One would hope that the teachers have sufficient self confidence that they would be willing to acknowledge that they are not the master of all the knowledge they teach, nor are they under any obligation to imply that they are in their dealings with students.