I now tackle the question of deduction namely: “if they didn’t spend their childhood together why are they both so good at deduction? Mycroft must have taught Sherlock!”
Deduction as a skill is really not rare. It’s not something the Holmes Brothers have in common with just each other but something they have in common with a great deal of people.
Deduction is a skill they didn't have to have learnt from each other.
“both of them felt the need to develop since a very young age (apparently, since their childhood) a VERY peculiar ability at “practical deduction” – thenorwoodbuilder
I completely agree that deduction is a peculiar ability for the Holmes brothers to acquire; but it’s actually not a very peculiar or rare ability.
It is definitely something that you can learn and if you’re incredibly intelligent you can learn it very quickly.
Why Sherlock would have been Great Spy or Doctor...
There are many professions that require practical deduction skills that the Holmes Brothers display. I’m just going to use two as examples spies and doctors.
MI6/MI5 train all their intelligence field officers on the “peculiar” ability of being hyper-observant (which is a related skill set), so observant the things that they notice seem almost supernatural, and their intelligence officers are not all geniuses. They don’t just look at the objects on a person; they learn to read people’s hidden emotions through their expressions, the subtle movements of eyes etc. Like professional gamblers they are trained to find your “tell” and then ruthlessly exploit it (for the safety and security of the country).
Interrogations experts are trained in the art analysing individuals. There are techniques that work on everyone but the best interrogations are ones which are personalised. They deduce what makes you tick, in the same way Sherlock deduced why the cabbie went around killing people. Often they will have more information than Sherlock, but also a much more difficult task because the people they come up against may be professional spies or terrorists rather than…crooks.
Doctors deduce people every day but on a different set of criteria to the Holmes Brothers. It is said that in medicine when a patient walks through your door, you should already know what their diagnosis is. Obviously this is an over exaggeration but the art of making differential diagnoses in medicine is exactly the same Sherlock’s process of deduction except unlike on TV, deduction in real life is not quite the precise art Sherlock makes us think it is.
To give a few examples a paediatrics consultant used to be able to “miraculously” tell what the kids had for breakfast by listening to their tummies. I never quite worked out how she did but we all thought it was a combination of crumbs and the child’s breath.
A neurologist diagnosed his patients from his window as they walked through the car park. Obviously he never told his patients he already knew what was wrong with them and they could go home before they even set foot in the hospital.
The reason you never hear your doctor deducing you is because you are not a problem to be solved, you are a person (and also there aren’t that many spot diagnoses – most of you should not be visible when you see your doctor, certainly not your internal organs). Although in some cases we might be able to tell what your diagnosis just by looking at you we have no idea how your illness is affecting your life. As doctors it is important to support the patient socially, emotionally and psychologically.
Imagine for example you’ve been feeling run down, find it difficult to keep your eyes open and suddenly develop a nasty cough with some blood. You think you’ve got pneumonia, better see your doctor. How would you feel if your doctor, as soon as you came into the room said:
“I can tell by the muscle wasting in your hand, your drooping left eye lid, your constricted pupil, dry skin and blood stained tissue that you have an apical lung tumour. The tumour has eroded into a main airway and you have only months to live.”
(these are real features of a pancoast tumour and there are patients who present like this)
You’d be a) shocked and b) devastated.
The way that Sherlock casually spews information out at everyone within in earshot without ever checking his facts or thinking about the consequences of what he says is not, as John might think, brilliant. In fact it can have devastating consequences. How do you think the driver in ASiB would have felt when Sherlock diagnosed him with a serious heart condition as an aside?
Of course if you have the symptoms mentioned above you might not have a pancoast tumour, there are other things that cause some of these symptoms, together known as Horner’s syndrome. This is why we need to take a chest x-ray to confirm – the burden of proof is on the doctor.
Sherlock never has the burden of proof placed on his deductions – it’s the police who have to gather all the physical evidence for him. We don’t always find out if everything he has deduced is correct because there is no fact checking afterwards. In the show we are suppose to assume that he just is.
Deduction in real life is not the precise art that Sherlock makes it out to be. Although I am somewhat pleased to see the Sherlock mistook Harry for a man and never thought it could be a woman.
Side note - Carl's flaky skin. There are plenty of other dermatological problems that cause your skin to flake in much greater amounts than eczema and thus would be better conclusions. Conversely not all types of eczema cause shedding of skin - some of them present as blisters.
Eczema is usually confined to the flexures: wrist flexures and sometimes finger webs. You do not use your wrist or finger webs to tie your shoe laces. If your eczema is so bad your skin is practically shedding everywhere even without contact - you should be getting treatment, you wouldn't be able to tolerate it otherwise. So if Carl had bad eczema, there should be traces of steroid cream on his show laces not skin. (feel free to correct me)
So why does John think Sherlock is so amazing? He’s a doctor right?
Well to be honest I don’t actually think the writers understand, anymore than the average person, what doctors do, or how they think.
But for an in-universe explanation – John is a GP. His patients usually come in with really rather vague symptoms that no doctor can get to bottom of just by looking and listening. Whereas in neurology and dermatology there are many spot diagnoses (and also plenty of things that utterly baffle). GP patients often have complex psycho-social problems that manifest as physical symptoms without logic or explanation.
Also John has learnt to deduce medical phenomena only. Also patients are entitled to their privacy and using your skills to deduce the state of someone's marriage when its no relation to their medical condition is unethical.
To meet Sherlock who seems so confident and correct in his deductions, John must be impressed because he knows how much of an imprecise art deduction can be. Had John and Sherlock ever need to diagnose a patient - well then John would look much better.
Learning the Art
There is no particular reason why deduction had to have been developed in childhood. The intelligence officers and doctors didn’t start practicing as children but it doesn’t make them bad at deduction.
Sherlock and Mycroft are incredibly good at deduction but to be incredibly good you do not necessarily have to have done something over a very long period of time. One important factor of intelligence is how quick you can absorb new information and given how intelligent we all agree the Holmes Brothers are, a short intense period dedicated to perfecting the art may be all they need to master it and continued use of deduction in their careers prevents their skills from rusting. Also learning as an adult is very different to learning as child. You have more drive and definitely more focus, which will enable you to master something you want in a shorter time period than a child.
I would also like to point out deduction is not an easy skill to develop by on your own without instruction not matter how clever you are. You need to learn to make the correct associations between what you observe and what you conclude. You also need to learn where to look and what to look for. If you make one wrong association your entire conclusion goes to pot. Learning deduction by trial and error is an incredibly arduous process with no guarantee of success. This is because if you are learning on your own, there is no one to check your conclusions, give feedback, facilitate reflection of what you would do differently next time - which are all very important for association focused learning.
The problem with calling deduction a science is that although it has a methodology, this cannot be applied to all deductions. Some associations are not the common-sense type that Sherlock blurts out, they require specialist knowledge to deduce correctly e.g. ezcema. Other associations are just not logical in the slightest because you are deducing people and people are not known for their logical behaviour. Illogical deductions really are things you need to be taught/have pointed out to you.
For example one would not think to check for kidney failure if a patient is peeing more than usual but in fact in the early stages, this is a symptom of kidney failure. You can't make this association until you've been specifically taught to do it.
This is why I don’t think Mycroft learnt how to deduce people on his own and then taught Sherlock but they both learn this skills in later life.
Deduction is certainly a very useful skill but that does not mean it was developed by the Holmes Brothers in self-defence or with their future careers in mind. In fact had Sherlock never developed this skill, less people would have wanted to punch him and his relationships might have been less fraught. Once again, deduction is something Sherlock likes to do in order to show off how different he is to everyone else. In the same vein Mycroft also uses this ability to awe and intimidate.
It appears to be something that the Holmes Brothers enjoy – it’s almost like a very useful hobby. Look how happy Sherlock and Mycroft are deducing John’s night at Sarah’s in TGG.
I think this is the only interest the two of them have in common and something that anchors their relationship through the turmoil.
A Niche for every type of Misfit
This hobby, like having similar professions, does not automatically make them similar people that shared a close childhood. I turned up to University to discover that there was an entire group of people who went around assassinating complete strangers for fun! Well obviously no one really died but that was one peculiar hobby.
Were they all siblings? Did they all share traumatic childhoods that meant they now felt the need to spend huge amounts of their time ruthlessly hunting down and pretending to kill strangers?
No, they were a very diverse bunch of people, some of who were quite nice (after they had wiped you off their to-kill-list).
When these people leave university – their employers/families/flatmates are incredibly creeped out by the abilities they have developed because there is no reason on earth why these young people should be able to do some of the things they can (scaling sheer surfaces being one of them). Other people will start to find ways to explain why their employee/child/flatmate spent their university years pretending to kill people for fun. Certainly a set of three siblings who all went to work for the same company were inundated with requests to see the resident counsellor about their shared “traumatic childhood”. We found this incredibly funny because they came from perfectly normal (rather boring) middle class family.
As one assassin pointed out: just because he goes to the same student society as his sister, doesn’t make him a warped male version of her. He joined the assassins’ guild not because he made the same decision as his sister – but because he made the same decision as the two hundred other members.
I don’t see why Sherlock and Mycroft might not have been engaged in a “deduction club” at University. There are some very crazy student societies out there – Cambridge, I believe, has a niche to fit every type of misfit.
Amendment in response to thecutteralicia. Click here to read: full response
Sherlock most likely went to a different University to Mycroft but both I believe went to Oxbridge (Oxbridge - Camford, Sherlock’s university life)
Hence Sherlock could easily have discovered a deducting club at his university and he wouldn’t ever be haunted by the spectre of his older brother or be accused of following in his footsteps.
There is no evidence that Sherlock completely shuns things he enjoys just to spite Mycroft. On the surface he refused to take the case in TGG but he did go about solving it anyway. He doesn’t refuse to take the case in ASiB because it intrigued him. Hence there is no reason why Sherlock wouldn’t join a deducting club, particularly if the club had never even heard of Mycroft Holmes
Sherlock was seen as lone weirdo by Sebastian (and probably the rest of his college) because he blurted out all his deductions of people’s private lives without any thought to the consequences. I do not think Sherlock was hated and alienated because of his skills but rather because of his vocal demonstration.
I very much doubt Mycroft ever voiced his deductions outside the club unless he would gain something positive. Most people who have “unusual” hobbies do not also have a completely lack of social skills that makes their hobbies incredibly annoying to others. The assassins don't attempt to murder people not "in the game" as it were. Sherlock's combination of hobby and lack of social skills it what makes him effectively friendless.
Mycroft makes the case that Sherlock had no "school-friends". This does not mean Sherlock didn't have friends at university or at least less enemies. Firstly Sherlock's personality is really not that extreme on the Cambridge spectrum, there are plenty of people who are very like Sherlock wandering around. They unfortunately aren't all in one college, or one staircase. Due to the college system they do find themselves segregated from each other and surrounded by people who are what the rest of the world would call "normal". It is the existence of University clubs that helps like minded people outside of their colleges. Just because Sherlock did not get on with the people he happened to live with i.e. Sebastian, does mean he would not have enjoyed his time at university. I have personally met many people who would make Sherlock seem like paragon of social grace and from my personal experience, Sherlock would have found a niche in Cambridge and really enjoyed himself.
Well why not? It's not surprising Mycroft is better at deduction than Sherlock, he's generally more intelligent or at least intelligent in a different way. He also has had more experience with people to be able to form his own set of connections between observation and conclusion.
Sherlock is learning deduction skills from Mycroft now that they are seeing quite a lot of each other. This doesn’t mean he first learnt them as child from his brother who developed the skills himself. Their shared love of deduction may have been the only common ground they had as adults but that was something Mycroft built on during their bonding as adults.