Abduction is the inference to the best explanation, that is, after using Induction, we may find ourselves faced with two or more explanations, we generally use abductive reasoning to choose the simplest explanation over any complicated explanation (i.e Occam's Razor).
Let’s go back to Pegasi, let us suppose that we were walking by the seashore, and found some horse footprints.
Now, these footprints look like a Pegasus footprints, and we may be inclined to support our hypothesis that Pegasi exist, and these footprints are evidence that supports our hypothesis.
This may actually look like a good piece of evidence (albeit not in the subject of Pegasi, but in more tricky subjects like Intelligent Design). The problem is that there is a simpler explanation, which is a “horse”
We already saw horses before .
We never saw Pegasi before.
We already know, by induction, that horses have such footprints.
We know by analogy that Pegasi have also such footprints, since they are analogous to (or resemble) winged horses.
Therefore, it is more likely that this is a horse footprint and NOT a Pegasus.
Of course it is still possible that this is maybe a Pegasus, but the simplest explanation is a “horse footprints”, so we stick to the simplest explanation.
This is how Abductive Reasoning works, let's see another more realistic example.
There are at least two ideas concerned with the appearance of species, one of which is a Scientific Theory (Evolution).
Personally, I have a good reason to think that Evolution by Natural Selection is very simple an explanation to account for the emergence of different species on earth. Why is that?
I will use Abduction in my argument, this is my string of thoughts on the subject.
- Premise 1: by induction, species appear slowly and gradually in the fossil record AND they are genetically related in a gradual manner, that is : some species are more closely related than others, in a way that is consistent with what evolution predicts.
- Premise 2: IF that (Premise 1) is the case, THEN Either a deceptive Intelligent Designer who slowly and gradually created one species at a time in a way that looks like gradual evolution OR life has evolved.
- Conclusion 1: Either a deceptive Intelligent Designer slowly and gradually created one species at a time in a way that looks like gradual evolution OR life has evolved.
Now you may agree with Conclusion 1, that either what you see in the picture below is done by an Intelligent Designer (who tries to deceive scientists into thinking that evolution is true), OR by evolution of most ancient species to new species and life forms. It seems like we have a premise for our next argument.
This is my second argument that uses "conclusion 1" as a premise.
- Premise 1: Either a deceptive Intelligent Designer slowly and gradually created one species at a time in a way that looks like gradual evolution OR life has evolved.
- Premise 2: I think the evolution of life is simpler an explanation than a deceptive Intelligent Designer who slowly and gradually created one species at a time in a way that looks like gradual evolution
- Conclusion: Therefore, by abduction, Evolution is the best explanation.
Why do I think evolution is simpler explanation than an intelligent designer?
Well, in the same way I do not think that yesterday is just a false memory created in my brain by an Intelligent Designer who tries to deceive me into thinking that yesterday's memories are true, It is the same logic.
Of course, it is possible that the fossil record and genetic evidence, and yesterday's memories, are all part of a great deception and conspiracy. But these ideas are quite complex as they suppose too much, therefore, by abduction, they are probably false, since the simpler ideas are that the fossil record, genetic evidence and yesterday's memories, are all better explanations that evolution happened, and that yesterday's memories did happen, no conspiracies.
So far, We saw 3 types of reasoning : Deduction, Induction and Abduction. To recap:
- We use deduction to create logically consistent structures and models : If fossil record and genetics show such and such, then Evolution or Intelligent Designer did it.
- We use induction to see if it is the case, by observation and experiment, if the premises hold. Yes, the fossil record and genetics show such and such. Therefore Evolution Or Intelligent Designer probably did it.
- We use Abduction to refer to the best explanation, we can show that evolutionary mechanisms are simpler than conspiracies and deceptions.
That's how the scientific method works in part.
Now, as we have seen three types of reasoning, this is it for this lesson. In the future, we will see other types of reasoning: Retroductive, Indeductive...etc
In the next lesson I will walk you through different distinctions like Analytic / Synthetic statements, A priori / A posteriori knowledge ...etc, the topic that maybe will take 2 lessons.