The following is a guest post by Glenn Dolphin (aka "Flipper"), of the University of Calgary Department of Geosciences.
This discussion first appeared in the ESPRIT list server, a lively forum for discussion of earth science teaching, mostly at the secondary school level. When Flipper's ideas below came forth, there had been an extensive multi-person, multi-day discussion of whether it was useful or misleading to tell students, during their study of weather and climate, that "warm air holds more water vapor than cold air." Although this and synonymous statements are common in popular science treatments (for example, here), this form of explanation has been roundly criticized in other expositions for the public (for example, here and here).
A point of view held by several teachers could be summarized by one who wrote: "As I see it, declaring that air 'holds' water isn't nearly as awful as it's made out to be." I was reminded of my blog post and followup comments about Telling Lies to Children, asking where is the borderline between a pedagogically valuable simplification and a lie. Air "holding" water is not literally true; it is a metaphor in which air is compared to a container with a limited holding capacity. Metaphors can be valuable tools for helping the human mind come to grips with (another metaphor) an unfamiliar concept. But they also have pitfalls, as explored in the guest post below.
-----Kim Kastens--Earth & Mind co-editor
Guest blog post
In my research, I am looking at the metaphors we (experts, for the most part) use in science and their effect on how students (novices) understand them. We use many metaphors (selfish gene, black hole, big bang, electron cloud, tectonic plate). As experts, we may very well be able to use "hold" if we have a good physical understanding for the air/water system. However, people who don't, like our novice students, will generate meaning based on their own physical experiences of containers that hold things. This could then lead to difficulties in understanding, most likely because they will always start from this point, and not give other meanings a chance.
Is there any research demonstrating that students using this container metaphor actually think of air as a bounded volume? There is none that I am aware of. However, there is quite a bit of literature on student misconceptions in earth science and that many of these (if not most) are the result of utilizing common every-day experiences with scientific concepts. So, for instance, the misconception that groundwater occurs mainly as underground rivers and lakes, does not come from the instruction they get (at least I am assuming) but from the common experience that water occurs at the earth's surface in the form of lakes and streams and since students do not have the common experiences of water traveling through the pore spaces of sediment, they rely on their experiences of rivers and lakes to define their understanding of water under ground. This literature is reviewed by Kim Cheek (2010) and Mark Francek (2013).
There is plenty of research supporting the idea that humans use metaphors, not as literary, artistic devices, but as a way to understand abstract concepts through our embodied experiences (Grady, 1999; Kahneman, 2011; Lakoff & Johnson, 1980, 1999; Reddy, 1979). The premise is this: We can only know our surroundings through concrete embodied experiences. That is just a fancy way of saying "through our senses". Because we cannot concretely experience abstract concepts, such as love, we rely on assigning meaning to that abstract concept through the only knowledge we have, our concrete and embodied experiences, through the use of metaphor. We learn about our surroundings as infants from grabbing ahold of things and sticking them in our mouth. This concrete, embodied experience leads to meaningful use of metaphors like "I've got a grasp of how to do this, now" and "If you spend half a day at it, you'll get a taste for how it is done." We come to know through other senses as well, making meaningful sayings like, "the detective is hot on the scent." Or " I hear what you are saying." Or "It's all very clear to me now." In the case of love, we might use the metaphor that a loving relationship is a journey. In which case saying things like "traveling through life together", "I'm only going along for the ride", "it was a dead end relationship" all make sense and convey what we are feeling, but in terms more concrete to us.
The amazing thing is that the brain does not perceive the metaphor as an artistic tool, but actually, and unconsciously, as the actual experience. Kahneman (2011) has numerous examples in his book where participants in psychological experiments were unconsciously affected by the use of such verbal cues. For instance, having been exposed to the concept of "old", in an implicit way, caused participants to move more slowly when walking, due to their perception of what "old" means.
I am currently working on publishing research that suggests that the metaphor "plate" in "tectonic plate" may be an inhibiting factor in students' development of meaningful understanding of earthquakes and plate tectonics. At issue is the idea that "tectonic" has no meaning for a novice, but "plate" holds a strong and common meaning because we eat off of them daily. They are separate entities and we can push them together and stack them up and we can break them if we drop them because they are brittle. However, tectonic plates are not separate from each other, and they can withstand a certain amount of elastic deformation before breaking, and they can even deform by folding and stretching. My participants had a great deal of difficulty attributing elastic properties (the cause of earthquakes, mind you) to rock, or plates, I would say because that is not their everyday experience with plates. I would further assert, strongly, based on others' works on metaphor and perception, that just because we say it is different, there is still an unconscious understanding derived from the everyday meaning of the metaphor, unconsciously. This is why many misconceptions go unchanged, even after direct instruction ((Blake, 2005; Clark, Libarkin, Kortz, & Jordan, 2011; Dodick & Orion, 2003; Libarkin, 2005; Libarkin & Anderson, 2005; Marques & Thompson, 1997; Orion & Ault, 2007; Posner, Strike, Hewson, & Gertzog, 1982; Sibley, 2005; Strike & Posner, 1992; Wandersee, Clary, Anderson, & Libarkin, 2003). To try and mitigate this, I will be researching the use of a new metaphor for the lithosphere, the "lithosphere as skin of the earth" for its quality of wholeness and flexibility, prior to utilizing the word plate.
Getting back to the "air as a container" metaphor, we often use a bounded volume as a metaphor, again, because we have a great deal of embodied experiences with this. We say water is "in" a lake, but technically that's not true. The lake is just an extension of the water table above ground level. It is not a container, like a pool is a container. We say we are "in" love. Physically, it makes no sense to be "in" an abstract concept. But there have been some neurological studies giving evidence that thinking about a container in an imaginative way (the cell is a container, the atmosphere is a container) activates the same parts of the brain as physically exploring a container or insides of cups (Gallese & Lakoff, 2005).
For the "air is a container" metaphor, we can predict meaning from the strong (embodied) experiences with containers being filled to top or running over, strong experiences with "holding", experiences with "saturation" (He stood out in the rain until he was saturated), and experiences with "squeezing" things (like sponges) out. Saying that warm air can hold more water than cold air, or that the dew point is when air is saturated, or cold air is drier because the water gets squeezed out of it, may highlight the correlation we observe that warm air is generally more humid (in an absolute sense) than cold air. However, that same metaphor hides many other important aspects of the phenomenon:
- First, air has plenty of room for water vapor,
- Second, gases do not interact with each other,
- Third, clouds form due to adiabatic cooling (cooling from expansion and not compression as is implied by the container metaphor), and
- Fourth, the notion of dynamic equilibrium between evaporation and condensation.
It is a powerful metaphor, but in terms of teaching, it hides far more than it highlights.
The metaphor is a powerful psychological tool. In fact, according to their research in the history of science, Müller-Wille and Rheinberger (2012) stated that "the lock and key... key principle...acted as an 'epistemological obstacle' to the molecularization of genetics...as its vivid imagery made it hard to adopt a different and new perspective" (p. 163). So, even for experts, it may be hard to step out of the limitations of the metaphor.
Though you as an expert state that you do not see air as a container, a bounded volume, you are an expert with a world more of experiences to buttress the meaning you have made when you use that phrase. When novices come in our room, they have the raw materials of their own personal experiences to begin making new understandings. Just telling them will not make them see the limitations of those understandings ( I direct you again to Michael Reddy's treatment of the "conduit metaphor" for communication). They need to have more powerful experiences to replace what their normal default would be. We need to find common metaphors that more closely resemble the meanings we wish students to have. I guess my point (finally) is that metaphors are strong (and subconscious) influences on understanding. Just because we (experts) can see the limitations (or can SAY we see the limitations), doesn't mean our students (who are novices, not knowing what they don't know) can also see the limitations. Why should we use language that is at best confusing, and at worst, just physically wrong, when we could easily be clear and use language that is more suitable at invoking what we want students to learn?
- Blake, A. (2005). Do young children's ideas about the earth's structure and processes reveal underlying patterns of descriptive and causal understanding in earth science? Research in Science and Technological Education, 23(1), 59-74.
- Cheek, K. (2010). Commentary: A summary and analysis of twenty-seven years of geoscience conceptions in research. Journal of Geoscience Education, 58(3), 122-134.
- Clark, S., Libarkin, J., Kortz, k., & Jordan, S. (2011). Alternate conceptions of plate tectonics held by non science undergraduates. Journal of Geoscience Eductation, 59, 251-262.
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