This is not an original metaphor. I don’t remember where or when I first heard it nor do I know who first came up with it, but it has become a favorite. I introduced it through the first week of school and come back to it again and again through the year.
It is a metaphor of an iceberg. The iceberg we see is huge, majestic and foreboding, all at the same time. That iceberg that we see, is only 12 % of the iceberg that is there. The other 88% is resting silently and hidden under the water. (The science behind it is explained well here. http://www.bsharp.org/physics/icebergs)
This image of an iceberg becomes a metaphor when you think of it as an idea, a thought or an argument. The portion above the surface is the obvious part, but the majority is hidden, the depth of it is not obviously visible. When a student offers me an abviose answer I often just ask, what’s below the surface? or, think deeper. It becomes our own little key word to trigger a habit of looking beyond the obvious for the underlying assumptions. It has obvious implications for TOK but I use it in grade 5 and grade 2.