The water trough was missing in the barn lot and the animals were in disarray. The chickens were positive that turkeys had stolen it because they said the turkeys always looked rather shifty. The turkeys said a group of rats had been sneaking in at night to steal food and must have taken the waterer. Fights had already broken out and a turkey and chicken had already been arrested and moved to solitary cages. If the sheep came in from the pasture, parched and thirsty, and found no water trough they wouldn’t care who took it and would hold every one responsible. Nobody wanted their wrath. Someone needed to solve the mystery, return the waterer, and do it quickly.
Only one duo could solve this. Sheeplock Holmes and Dachson were on the case. Upon arrival, Sheeplock quickly hushed the gathered animals, took a long chew of his cud and surveyed the lot. Dachson tried to talk but was shushed. With a triumphant flourish, Sheeplock turned to the watchers and said I know what happened to the waterer. It was not the chickens, the turkeys or the rats. Dachson looked perplexed, as did everyone else and said But Sheeplock, there’s no one else here. How could someone else have taken it? Sheeplock looked smug and winked before stating There are human footprints leading from the gate to the waterer and then drag marks and more footprints leading back to the gate. The only obvious solution is that the humans took the waterer to clean it and will return it shortly with fresh water. I have correctly deduced what has happened! The animals all applauded, except for Dachson who had to say But Sheeplock, that’s not deductive reasoning, that abduction.
For all his bluster and even though he was probably right about who took the water, Sheeplock was wrong about the type of reasoning he used. He thought he was using his powerful deductive skills but that’s not what he did here. In fact, he used a method of reasoning known as Abduction. Deduction is a type of reasoning, along with Induction (and if you’d like, conduction which is where you think so hard you generate heat). Abductive reasoning is when we start with a set of observations and look for the most likely explanation. As the fictionally real Sherlock Holmes liked to state when you have eliminated the impossible, whatever remains, however improbable, must be the truth. In a nutshell, this is abductive reasoning. We observe some given scenario, exclude anything that is impossible and then from what remains choose the most likely.
Unfortunately for Sheeplock (and Sherlock) abductive reasoning does not always produce the truth. This type of logic will produce what is most likely the truth. It is quite possible that the waterer broke and the humans took it away but do not have another one to replace it with. Perhaps someone else did drag away the waterer and the footprints were from the humans trying to figure out what happened. Maybe a new frost-free waterer was getting installed. Lots of other things could have happened that were not impossible. While this is a valid form of reasoning, and something we all regularly use, we should be careful with it.
Let’s look at another example. You are awoken at night by a strange groaning or creaking like noise. Investigating, you confirm that you are alone and you have no pets to create such sounds. You can find nothing structurally wrong with the house or indeed anything out of the ordinary. There doesn’t seem to be anything going on outside. You can use your abductive reasoning to rule out alien visitation, ghosts or even something having snuck into the house so the only likely explanation is noises from expansion and contraction that occurs from temperature changes. Feeling smart, you go to sleep and wake up to a very cold house. While your abductive reasoning gave you the most likely answer, it wasn’t the correct one. You are not an expert in heating systems and the noise was the furnace failing. Time to call a repairman.
Some people use abduction regularly to do their jobs. If you visit your doctor with a problem, they’ll ask you a series of questions to determine your symptoms and from the answers they’ll look for the most likely problem. If you have a fever, chills, body aches and its flu season then you most likely have the flu and they’ll treat you for that. It’s unlikely you are in the early stages of werewolfism. If you don’t respond to treatment and return later with a lot more body hair, the diagnosis might change. Consider how a detective works on a crime – they look at all the evidence, eye witness testimony and crime scene analysis to come up with the most likely explanation which they can then track down. If they catch someone, but that person has a valid alibi, then they start over. We know with both doctors and detectives that when abductive reasoning is used, they can get it wrong.
Now you know about one of the 3 types of reasoning – Abduction. You can use this to find the most likely explanation to a given scenario but it may not be the right explanation. Sheeplock (along with Sherlock) have probably made us think this is really deduction, but that is something different we’ll look at later, along with inductive reasoning. I’ll bet that if you examine your thinking, you’ll find many times you use abductive reasoning. Luckily for the animals, the humans were replacing a cracked waterer, they just needed time to go out and purchase one. By the end of the day there was plenty of fresh, clean water when the sheep came in.