On one hand, no one in the world enjoys pedantry but, on the other, the world has had it coming. A simmering rage has been bubbling within me and a facebook advert has just made me snap. I can contain myself no longer.
The advert in question is for a t-shirt for Monty-Python fans:
Anyone who has seen Monty Python and the Holy Grail will know that it refers to the famous witch-burning scene which hilariously relies on logical fallacy to concoct a test for witchness: If a thing weighs the same as a duck then it must float. If a thing floats then it is made of wood. If a thing is made of wood it will burn. Witches burn. Therefore, if a thing weighs the same as a duck, then that thing is a witch.
Ludicrous. Nonsense. All very funny.
What I don't find funny, however, is the ham-fisted attempt to render this in the Venn diagram appearing on the above t-shirt. You can't just take some of the key-words, put them hap-hazardly in a diagram of intersecting circles, and produce a meaningful graph. It's utter nonsense (maybe that's the point but venting ire is therapeutic so please humour me).
There seems to be an increasing fad for misusing Venn diagrams in internet memes. This one was merely the offending straw that broke the camel's back. I could just let it go, but I see students misunderstanding these diagrams every year in the same way the designers of this t-shirt have.
Let's start with basics: A Venn diagram contains a number of circular (or other shaped) regions and each contains a well-defined collection of thing. The diagram is contained within a region that might represent the set of all the objects - the universal set - that are being considered. For example, if the universal set is the positive integers from 1-10, then the following Venn diagram is valid:
Granted, you wouldn't put it on a t-shirt but at least it makes sense.
One problem with the Monty-Python Venn diagram above is that the sets are misleadingly labelled. Suppose I'd written the following:
This is too slapdash as the moon-shaped segment on the left is not the only place where even numbers can be placed. It may seem pedantic but a lack of clarity here is, in my experience, the number one source of error when students tackle Venn diagrams in school.
Here are examples of several Venn-memes that make me squirm for this reason:
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| No! |
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| NO! |
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| NOOOOO! |
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| OH GOD! WILL SOMEBODY PLEASE THINK OF THE CHILDREN |
It seems that one Stephen Wildish is a particular purveyor of non-Venn diagrams. He seems to have made a book full of them. I won't be buying it.
If we are insistent on labelling every region individually then this is how to do it:
Granted, it isn't as snappy, but it does give an accurate description of those objects that appear in each region. Unfortunately, its lack of snappiness means that correct Venn diagrams don't particularly lend themselves to their adopted use as memes. Most correct maths just isn't funny and most funny maths just isn't correct. It's a conflict that seems unresolvable. This is a shame because it would be very pleasing to end this post with a mathematically sound comic Venn.
Back to the Monty Python chart, though. I'm not finished with that. Supposing instead that the words are actually elements of the set instead of descriptions of their contents, we encounter a further problem. Take the top green set for example. It contains the elements, "witches", "same weight", "burn", "made of wood". I defy anyone to come up with a single category that these could fit into: One is a plural noun, one a comparison, one a verb, and one acts as an adjective. It's like the hardest game of only connect ever!
So I have decided to take a stand.
Every time I am subjected to a terrible Venn diagram on my facebook news feed I will comment with a link to this blog post. Anyone who bothers to read to the bottom will witness my venngeance expressed in the following passive-aggressive manner:
from matheminutes http://ift.tt/2eMY5Oz
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