Inference to the best explanation/abductive reasoning

You have just finished shopping at your local shopping centre. You head down to the parking lot and discover that your car is missing. From this, you conclude that your car has been stolen. In standard form, this would be the reasoning:

  • My car is not here
  • Therefore,
  • My car has been stolen

Of course, this reasoning is invalid. It could be possible that you have forgotten where you parked it and are looking in the wrong area, your spouse has played a trick on you and moved the car without your knowledge, or aliens have vaporised your car. However, you will probably reject these explanations and accept the explanation that the car was stolen.

This kind of reasoning is known as abductive reasoning, or otherwise known as ‘inference to the best explanation’. This is how some philosophers will approach the argument:

  • 1. My car is not here
  • 2. The correct explanation for this is that my car has been stolen
  • Therefore,
  • 3. My car has been stolen

The problem with this approach is that it begs the question, because we cannot accept premise 2 without already accepting premise 3. Here is an approach which does not beg the question:

  • 1. My car is not here
  • 2. The best explanation for this is that my car has been stolen
  • 3. The best explanation is the most probable explanation
  • Therefore,
  • 4. My car has probably been stolen

This is valid, however it has a weakened premise. It must have a weakened premise because there will always be an alternative explanation which cannot be ruled out. We can, at least in principle, rule out parking the car in the wrong area and our spouse playing a trick on us, but we cannot rule out aliens vaporising the car.

What makes something the best explanation?

Explanatory power

An explanation which is explanatorily powerful is when the explanation satisfies all the things that need explaining. In philosophical jargon, the things needing explaining is called the explanandum, and the explanation for those things is called the explanans. The form of such tests go as such”

  • 1. If my car has been stolen, my car will not be here
  • 2. My car is not here
  • Therefore,
  • 3. My car has been stolen

Of course, as we have established when we covered conditionals, this commits the fallacy of affirming the consequent. The other proposed explanations could be possible. However, we can increase the probability of the proposed explanation being true by ruling out competing explanations. We can rule out being parked in the wrong spot by checking our ticket or surveying the wider area, or calling our spouse to say “c’mon, the jokes over!”. However, we still cannot rule out aliens vaporising the car.


An explanation can be seen of value by how testable, or falisfiable, it is. This concept was popularised by philosopher of science Karl Popper. Popper’s view, according to A. F Chalmers (2013), is that explanations used in science can only be seen as truly scientific if they are based on bold predictions that can be easily tested and prove false, hence falsifiable. This motivated by the acknowledgement that any explanation can be explanatorily powerful if we have a good enough imagination, but only some of those explanations can be put to the test. The explanations of the spouse playing a trick and the car being in the wrong area are better competing explanations than the aliens vaporising the car, because they can much more easily be tested and proven false.

Background knowledge

An explanation can be better, and more probable, based on how much the explanation fits with similar situations we know do occur. This is saying how well it fits in our background knowledge. We know people will not find their cars due to them being stolen and forgetting where we last parked them, but not so much our spouses playing a trick on us, and much less aliens vaporising them.


An explanation that requires the fewest number of extra assumptions in order to adequately explain what needs explaining is called appealing to the explanation’s simplicity. This is sometimes called ‘Ockham’s Razor’. A complicated explanation is one that involves many assumptions, whilst a simple one involves only a few, or sometimes just one (it will always involve at least one, because inference to the best explanation is involving explaining something that hasn’t been observed based on things that have been observed).

Say we checked with witnesses and they said they saw someone suspicious entering your car. And the person proposing the spouse playing a trick on you says maybe they hired someone to do it, gave them the keys, and so on. This is a much more complicated explanation than someone stole your car.

Putting them all together

There are many other criteria scientists and philosophers will consider, and there is some controversy on how much value and what it says regarding the explanation’s actual probability, but this is a reasonable start.

It should be noted that the best explanation may not need to satisfy all the criteria. There may be an explanation which is less simple but more powerful, or one that is falsifiable but does not fit with our background knowledge, and so on. But we can compare these criteria and see which one does the best overall.

Test question

Try to see if you can see what is the best explanation (and why) from the following observation (have some fun with bad explanations as well):

There is rattling in the roof. I also hear scratching and squeeking.

I highly recommend ‘What is this thing called science?’ by A. F Chalmers if you wish to learn more regarding this topic. And also ‘Understanding arguments’ by Walter Sinnott-Armstrong and Robert Fogelin. If you purchase these books via the link below, you are supporting this website. Thank you.

Understanding arguments:

What is this thing called science?

Published by

Andrew Tulloch

I have a Bachelor of Arts majoring in Philosophy and Sociology, with a Political Science minor. I also have an honours degree in Philosophy. I am currently studying for my PhD in Philosophy.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s