Abductive Reasoning: A Primer

When you’re trying to explain a situation and there are several possibilities, which one do you choose?

This is where 'abductive reasoning' comes in.

The book The Philosopher’s Toolkit provides a great overview of the philosophy.

What is abductive reasoning?

Abduction is a process of reasoning used to decide which explanation of given phenomena we should select, and so, naturally, it is also called ‘argument to the best explanation’.

In other words, a method of deciding which explanation is superior.

Principles of Abduction

It must be noted that these principles are only tools. There is no way of knowing with 100% certainty which explanation is the best explanation. We can however, reach a closer probability of being correct. 

The main principles are:

1. Simplicity

When possible, go with the least complicated explanation, the one that requires the fewest and most direct causal sequences, the fewest claims about what exists, and that relies upon matters beyond the evidence as little as possible.

In essence, this principle is the same as Ockham's Razor.

2. Coherence

When possible, go with the explanation that’s consistent with what experts about the world already believe to be true.

3. Testability or Predictive Power

When possible, go with the theory that yields the most predictions that can be confirmed or disconfirmed.

That is to say, if investigation fails to confirm the prediction or finds an improbable absence of evidence, or if it fails to establish the existence of required entities, then the credibility of the hypothesis is diminished. Countervailing considerations such as disconfirming evidence or established knowledge with which the hypothesis cannot cohere diminishes the credibility of the hypothesis even further.

4. Comprehensiveness in Scope

When possible, go with the explanation that explains the most and leaves the fewest loose ends (or things unexplained).

Example

The Scenario

A man is found in a cabin in a remote forest, with all the doors and windows securely locked from the inside, hanging dead from a noose. A suicide note in the man’s handwriting lies on the table nearby.

Possible Explanation 1:

Perhaps the man was rehearsing a dramatic play about suicide, had locked the doors for privacy, and things had gone terribly wrong.

That explanation suggests the existence of a relevant play and perhaps would predict a script of the play to have been in the man’s possession. It also raises the likelihood that the man would have been something like a member of a theatre troupe or drama class, or told his friends that he was auditioning for a play and so on. If, however, after examining the cabin and the man’s home, interviewing his friends, checking local theatre groups, no such evidence is found, this explanation can be discounted. 

Possible Explanation 2:

Or perhaps the CIA has developed teletransporters. Using one, perhaps an assassin beamed into the cabin, killed the man, set things up to look like a suicide, then beamed out without ever opening a door.

[This] fails to produce confirming evidence: it requires the existence of an extraordinary machine, it is difficult to test and it does not cohere with our background knowledge about the technological abilities of the US government or, perhaps, about space and time.

Possible Explanation 3:

Perhaps a demonic spirit living in the woods nearby magically entered the room, killed the man and then vanished.

[This] requires us to believe in the existence of supernatural beings not required by the other explanations and for which we have no evidence.

Possible Explanation 4: (Best Explanation)

Suicide.

Suicide as an explanation, on the other hand, is simple. It requires us to posit the existence of neither supernatural spirits nor secret, illegal government operations involving unknown but improbably advanced technologies. It allows us to make predictions that can be tested. (For example, by looking for documentation of depression or likely causes of depression such as having recently been fired, bankrupt or divorced.) Unlike the actor theory the suicide theory doesn’t predict the existence of things (like scripts) that can’t be found. It is consistent with our background knowledge of common human behaviour. And it explains all the facts before us.

Source

The Philosopher's Toolkit by Peter S. Fosl and Julian Baggini