Parsimony: Separating the sheep from the goats, the wheat from the tares
at 12:51 pm on Monday, 8 March 2010
Scientists use several techniques to choose between alternatives when one or more alternatives seem similarly valuable. As people interested in controversial scientific subjects we can use similar techniques to help us make decisions about subjects for which we have little technical knowledge.
Examples of this rule include such ideas as:
- If there are multiple paths to the same result, the route with the least branches is probably the best.
- Entities should not be multiplied unnecessarily.
- Do not add causes when they are not necessary.
- Eliminate any assumptions that do not change the observable results (to here the rule is often called “Occam’s Razor”).
- Keep it simple, stupid!
- Less is more.
This rule defines a philosophical/scientific property called “parsimony”. Parsimony is sometimes called “Occam’s Razor” but the rule covers more situations than Occam did. I will use “parsimony” because “Occam’s Razor” is misused in popular writing (by many newspapers and cable and radio comentators)”. Occam’s rules applied only to situations where two or more propositions ended in the same conclusion.
As a revolutionary thinker and as a Franciscan monk, Occam was faced with many complicated explanations of natural events. His principle was, when there are two explanations for the same event, to remove the extra propositions from the more complex one. Almost always, in the 14th century at least, the extra propositions to be removed were supernatural. As you can imagine he got into a lot of trouble with the church.
The scientific term “parsimony” was introduced into English much later than William of Occam’s time. It merely used Occam’s Razor as a jumping off place. “Parsimony” was introduced into English in our sense in the mid 1800s, when dozens of Latin words were adopted to explain or name scientific matters. Modern science was erupting into all kinds of new areas that required new names, and scientists all over the world seem to have agreed, in principle at least, that any new names would be in Latin, since Latin was the closest thing us westerners have to a universal language.
So, where does parsimony differ from Occam’s razor? Occam’s razor is just a special kind of parsimony. Parsimony is used in modern science to clarify a much broader range of situations. Occam only applied his razor where two propositions resulted in the same conclusion. It was used to discover the better proposition.
But, parsimony can also be applied to two propositions that result in different conclusions. While Occam’s razor tests two propositions that deliver the same result, modern scientific parsimony can also test when there are two different results derived from the same collection of data. While Occam’s razor tests the propositions, parsimony can also test the results. In this blog we have an example of each kind of parsimony.
We can use classical Occam’s Razor to evaluate evolution, and we use the more general rule of parsimony to evaluate the climate change controversy.
Evolution and Creationism (or intelligent design, or whatever the people who do not accept the theory of evolution are currently calling themselves) are both propositions to describe the natural world of living things. Creationism claims to explain a lot more than just life. Sometimes, for example, Creationists throw in a red herring called “The Big Bang Theory”. By the way, I always use “theory” in the scientific or mathematical sense (as the highest and most general hypothesis to explain data) , rather than in the sense of “having an opinion”, such as in “My theory is that he ran off the road because he was drunk”.
What both propositions are trying to explain is the living world. Where did this wide variety of plants and animals and viruses, etc. come from? We all share the same body of facts: living things that can be observed, fossils of living things that once existed, DNA from both living and extinct life forms, embryo development of placental and egg-laying creatures, etc. Simply put, Darwinian evolutionists say all life arose, over millions of years, from earlier life forms, through a process called “Natural Selection”. Creationists say that it was all created in a relatively short time by a supernatural being.
The creationist argument requires a lot of explanation beyond the simple proposition. First, one must believe that the supernatural creator or designer exists. Since the theory of evolution explains the life forms adequately without the addition of the supernatural being, the theory of evolution is more parsimonious than creationism.
In general, the climate controversy arrives at two different conclusions from the same climate data. The climate change advocates believe that the climate changes being reported are real and represent a dangerous trend that requires considerable effort on everyone’s part to slow down. Some people, on the other hand, believe either that the data are meaningless, or that, while global warming might exist, but isn’t dangerous. They do , however, sometimes use data and claim that they are able to falsify the hypotheses of the climate scientists. Often they simply try to destroy the credibility of the persons doing the science.
To believe that global warming is not real or dangerous one would need to assume that the 90 plus percent of the scientists who work in the relevant sciences are wrong. This means that they are either dishonest and are knowingly misrepresenting the data, and that only a handful of people are pointing out their perfidy, or they are ignorant, and don’t know enough about climate to be making a judgement on the issue. One would ask, why would over 90% of the scientists from several different fields of study get together and agree to misrepresent the data from several centuries of climate-related data?
So. in a word parsimony means that the simpler explanation that describes the phenomenon is the best.
There is a simple form of parsimony that helps us take a short cut to forming a first opinion of conflicting controversial oponions. Bertrand Russell said:
“When the experts are agreed, the opposite opinion cannot be held to be certain;
“When [they] are not agreed, no opinion can be regarded as certain by a non-expert;
“When they all hold no sufficient grounds for a positive opinion to exist, the ordinary man would do well to suspend his judgement.”
Bertrand Russell, Let the People Think (1941)
In this blog evolution and climate change are of the first type. Remember that NO scientific proposition can be absolutely certain.
Nuclear energy and waste management are of the second type. The non-expert should probably not take any side until the problem becomes more clear.
The Origin of Life may be of the third type if you are not convinced by any of the experiments so far. I personally put this in type one or two.
Climate Change is really scary, now we have super typhoons and a lot of flooding going on some countries..;-.
It is odd, however, religious folks will claim that special creation is simple-God did it! and that’s that! without seeing the underlying complexity.
Jim Peavler: I saw a post on FB that Stanley Weinstein posted but did not see a way to comment or “like”. I will try to post that I would like to “friend” you. (What happened to the verb “befriend”?
Anything that smacked of the supernatural was the first to go with Occam. Supernatural intervention is impossible to verify, so is always irrelevant in scientific argument. Appeals to any form of god are verboten.