09.10.2026 Diary XXXIX Family resemblance: no single common thing

09.10.2026 Diary Page XXXIX

A rope's strength lies not in a single fibre running from end to end, but in the fibres being intertwined.

Friday. I was reading a symptom list and something caught my attention. The list consisted of nine items. For a diagnosis five or six of them were enough. Which five or which six did not matter.

I stopped for a moment and did the calculation. There are a hundred and twenty-six ways to choose five out of nine items. Two people can receive the same diagnosis and not share a single symptom.

This looks like a logical error. It is not. It is exactly what Wittgenstein described.

Game

In section sixty-six of the Philosophical Investigations Wittgenstein asks: what is common to all the things we call "games"?

There are board games, card games, ball games, Olympic games. Is there amusement in all of them? Look at chess, then at tic-tac-toe. Is there winning and losing in all of them? In a solitaire card layout played alone there is no winner. Is there competition in all of them? When a child throws a ball at the wall and catches it, who is the rival?

Wittgenstein's advice is very famous: "Don't think, but look!" Do not make up a definition; look at how it is really used. When you look you see not a common feature but overlapping similarities. Some games resemble each other in one respect, others in another, but no single line binds them all.

He names this in section sixty-seven: family resemblances. Among the members of a family, features like height, eye color, gait, temperament overlap and cross. None is common to all but all are in the same family.

The image of the thread

In the same section there is an image of a thread and I like it even more. A thread is not strong because one fibre runs through its whole length. It is strong because many fibres are joined end to end and twisted around each other.

Concepts are like this too. What holds a concept together is not a single common feature; it is many small similarities that hold each other.

This idea opposes the old philosophical tradition that tried to look for the necessary and sufficient conditions to define what something is. Since Socrates we had been looking for a single definition of "what is justice," "what is knowledge." Wittgenstein says that for most concepts there is no such definition, and that this is not a deficiency.

The symptom list

When I carried this idea over to ADHD something interesting happened.

The structure of the diagnostic criteria is exactly in the form of a family resemblance. On the inattention side there are nine symptoms, on the hyperactivity and impulsivity side nine. Six are enough in children, five in adults. Criteria of this kind are called polythetic, in the sense that a part of the symptoms, not all of them, is necessary.

The result: someone with the predominantly inattentive presentation and someone with the hyperactive and impulsive presentation can receive the same diagnosis and, by the criteria, not share even a single symptom. One drifting off, forgetful, leaving their tasks half done; the other unable to sit still, interrupting, impatient. Both are ADHD.

I wrote about this presentation in detail in the inattentive type article. What I notice here is that this is not a flaw, it is the nature of the concept.

The "do I have it" question

The first reaction of most people reading a symptom list works in two directions at once.

One side says "I have all of them." The other side says "no, only some, so I don't have it."

The second thought misunderstands the structure of the criteria. They do not all have to be present. But the first thought is wrong too: having all of them does not prove the diagnosis. A diagnosis is not made by the list alone; the severity of the symptoms, their duration, how much they show across settings and how much they impair function also count.

I emphasized this point in the symptoms in adults article: fitting the list is not enough, you have to look at the consequences.

Wittgenstein's idea gives a comfort for this picture. The sentence "I don't have typical ADHD" has no basis, because there is no typical ADHD. There is a family and its members resemble each other.

The danger: identity

This idea has a side effect and I need to write that too.

Family resemblance makes the boundaries of a concept flexible. A flexible boundary can take everything in. ADHD content on social media feeds on exactly this flexibility: a short, striking description catches some side of everyone. I took this up in the social media article.

Wittgenstein thought about this too. Family resemblance does not mean everything resembles everything. There is a boundary; it is just not sharp. The concept of game starts with chess and reaches a child's ball against the wall; but an earthquake is not a game.

The boundary being blurry does not mean there is no boundary. I wrote the same thing in another way in the Sorites piece.

For ADHD this means: the concept is flexible, but the criterion of loss of function draws the limit of that flexibility. Not the presence of symptoms but their consequences count.

Following a rule

In the same work of Wittgenstein there is another discussion close to family resemblance: what does it mean to follow a rule? On this site I wrote a separate text on rule following.

There is a link between the two ideas. Learning the use of a concept is not memorizing a definition; it is seeing examples and sensing the resemblances. A child learns the word "game" not by learning a definition but by playing.

Learning a diagnosis is like this too. Looking at a list years later and saying "oh, so this was me" is not grasping a definition; it is recognizing yourself within the examples. This recognition resembles joining a family more than a definition with sharp boundaries.

Meaning in use

Another sentence in the same work of Wittgenstein explains why this idea matters: the meaning of a word is its use in the language.

Instead of looking for a definition or an essence behind a word, you have to look at how people use it. Everyone who uses the word "game" uses it correctly without knowing a definition.

The word "ADHD" is used like this too. A physician uses it by looking at the criteria, a person on social media uses it to describe themselves, a family uses it to describe a child. The three uses overlap but are not the same. Asking which one is the "real" use may be the wrong question; asking which use is valid in which context is more useful.

This explains why medical criteria are decisive for the decision of a diagnosis: the legal and medical context fixes, as a rule, what the word will mean. In everyday speech the word stretches.

Late diagnosis and not recognizing

Something people diagnosed late often live through: having trouble recognizing other people with ADHD.

Some of the stories they read do not resemble them at all. Children who cannot sit still, who disrupt the class, who get punished. That person was never like this; they were quiet, absent-minded, someone who got by. When they cannot find themselves in the stories, they doubt the diagnosis.

Family resemblance gives a good answer to this doubt. In the same family it happens that two siblings do not resemble each other at all; both are the child of the same mother. Not finding yourself in the stories does not mean not being of the family.

I think that is why the site's Your Experience section is important. Not a single ADHD narrative but narratives different from one another standing side by side. Even if the reader cannot find themselves in one, they can find themselves somewhere in the net of resemblance.

The limits of the label

This philosophical idea has a warning too: a label is not the person.

The sentence "I have ADHD" means attaching to a family of resemblance and this is very useful: it provides support, information and a connection with a community. But the same sentence can also lead a person to define themselves only by this family.

In family resemblance membership is the result of overlapping similarities; it is not an identity card. Being a member of the same family does not mean carrying every trait of the family.

This is a useful frame: some of the symptoms I have, some I do not; some I never lived, some I lived a lot. This is not a deficiency, it is the family's own structure.

What I listened to today

Arvo Pärt: Credo.

From 1968, for chorus, piano and orchestra. It takes Bach's C major prelude and surrounds it with harsh, fragmented music. The piece was banned by the Soviet authorities.

When I listen to Credo next to Fratres it is hard to believe they are the work of the same composer. One passes through harshness and fragmentation; the other is calm, repetitive, almost motionless. I cannot find a single common surface feature.

But I know both are Pärt. Between them there is a road, and you can hear that road being walked step by step. Family resemblance works for a composer's lifetime too.

Tomorrow

Tomorrow is Saturday. Somewhere in the week I asked myself the question "someone like me," and today I saw that it does not have a single right answer. There is a family; I am inside it too.