Opening scene
A student comes up to you after class and says:
"My hips are closed, that's why I can't do this pose."
One sentence. It contains four separate claims, and all four are tangled together.
"My hips are closed" is a structure claim — it's about the shape of something in the body. "I can't do it" is a function claim — it says a movement can't be produced. Behind the sentence, there's also an unspoken capacity claim: the assumption that even if they tried, they couldn't sustain it. And the thing that most likely set all of this off was a symptom — a pinch, a pull, a discomfort, somewhere.
When all four get squeezed into one sentence, there's nothing left for the teacher to do — because each of the four has its own remedy.
If it's structure, you adapt. If it's function, you teach. If it's capacity, you load. If it's a symptom, you watch, and refer if needed.
If you don't know which one it is, you can't try all four and see which one works — because you'd be doing them all at the same time.
What this lesson covers
First we'll define the four words one by one and say which question gets you to each one. Then we'll show five typical situations where the four get tangled together; each kind of tangle has its own particular cost. After that we'll set up two simple tests that help you tell them apart — one takes seconds, the other takes weeks. In the master layer we'll see how these four axes match up with the tools in the teacher's hands. We'll work through sixteen examples. By the end of the lesson, when you hear a student's sentence, you'll be able to tell which axis they're speaking from.
Starting point
Y2.01 defined anatomy's job as "listing possibilities." This lesson gives you how that listing is done: the possibilities aren't random, they're spread across four axes.
We defined capacity back in Y1 — the ability to perform a movement again and again, at the same quality, without producing a negative result. That definition still holds exactly. We're putting three more words next to it.
The order of the four axes matters. Structure changes the slowest, symptom changes the fastest. In between are function and capacity; both can be trained, one on a scale of days, the other of weeks.
Mechanism
The four axes are independent. A finding on one doesn't prove anything on another. Mistakes come from exactly this independence being forgotten.
Let's look at five typical confusions, one by one.
First confusion: structure to symptom
The most common one. "Imaging found this, so this is the cause of the pain."
Second confusion: symptom to structure
The reverse. "It hurts here, so something here must be torn."
The location of the pain and the source of the problem aren't always the same place. And pain isn't a measure of damage; we'll take that up in detail in B3.
Third confusion: function to structure
"I can't lift my arm, so there must be a structural problem in my shoulder."
There are at least three separate reasons a movement might not be produced: structure might really be limiting it, the movement might never have been learned, or the person might be guarding against that movement. All three produce the same picture.
Fourth confusion: capacity to structure
"I get tired in ten seconds, my body isn't built for this."
Getting tired is capacity information, and capacity is the most trainable axis. The moment it's turned into a structural verdict, the door closes.
Fifth confusion: structure to function
"My hips are closed, that's why I can't do this pose."
That's the sentence from the opening scene. A structural limit really does close off some shapes of some poses. But that limit doesn't close off the pose's purpose — Y1's second principle comes into play here: the load-bearing action is preserved, the shape is adapted.
Two ways to tell them apart
Now, the most useful part. You can narrow down which axis a limitation is on with two tests.
This test doesn't prove anything, it rules something out — and ruling out is information too.
The second way takes time: progressive loading. If the limitation opens up over weeks, it was capacity. If it changes neither in a minute nor over eight weeks, structure becomes the stronger candidate.
Both are tests — meaning you change one thing and read the result. There's also an observation that accompanies these, one that changes nothing.
It matters to see why observation is weaker than a test. In a test you change one thing and read the result, which means you rule out a possibility. In an observation you change nothing; you just gather an impression, and an impression can be wrong. End-feel is therefore not a decision, but a sequencing tool that helps you choose which test to run first.
Reading the examples
Looking at the common structure of the examples, a single move shows up: every time, a sentence jumps from one axis to another, and the jump goes unnoticed.
The direction of the jump determines the kind of damage. Jumps made toward structure close a door — the sentence "my body isn't built for this" doesn't produce an action, it produces an ending. Jumps made toward symptom, on the other hand, make you intervene in the wrong place; a teacher focused on where the pain is never sees the place producing the load.
There's one more pattern. Almost none of the sentences that jump toward structure are the student's own; they were heard somewhere. From a teacher, from a health consultation, from a piece of paper. Y2.21 will take up this language separately, but let's say this now: once a sentence settles into a person's belief about themselves, taking that sentence back takes far longer than saying it did.
Master layer
An experienced teacher doesn't just tell the four axes apart; they know the tool that corresponds to each one, and they don't use the wrong tool.
Facing a limit on the structure axis, the tool is adaptation. A raised seat, a change of angle, a different way in. The goal isn't to get past the limit, it's to produce the load-bearing action in a different shape.
Facing a limit on the function axis, the tool is teaching. Changing the order, working in an easier position, breaking the movement into parts. Here the time scale is days and weeks.
Facing a limit on the capacity axis, the tool is dose. Repetition, duration, waiting, rest. The scale is weeks and months.
On the symptom axis, the teacher has no tool — there's watching, and referral when it's needed. Trying to "solve" something on this axis is a violation of the boundary we drew in Y2.01.
The cost of the wrong tool isn't abstract — it's measurable in both directions.
The master's second subtlety is quieter: in most cases, you can't know for certain which axis a limit is on, and you can work with not knowing that. You start from the most likely axis, run the cheapest test, and read the result. Waiting for certainty means never starting.
Common mistakes and misconceptions
Common mistake"If there's a finding in a structure, it's the cause of the complaint."
Structural findings are common in people with no complaint at all. A finding is a candidate; causation has to be demonstrated separately.
Common mistake"The location of the pain is the location of the problem."
The region where pain is reported and the region producing the load are often different. A correction that only looks at the painful spot leaves the cause right where it was.
Common mistake"If I can't do a movement, my structure isn't suited for it."
The same picture can come from an unlearned coordination, from reduced capacity, or from guarding. Structure is the option left over once these three have been ruled out.
Common mistake"Capacity is a result of structure."
Capacity is the axis that changes the most; with the same structure, it can multiply within months. Reading structure as fate makes the most trainable axis invisible.
Common mistake"You can't intervene without knowing which axis it's on."
Just the opposite: most of the time, it's the intervention that reveals the axis. The right thing isn't to wait, it's to run a cheap, single-variable test.
Practice
Keep in mind
Four words, four separate questions. Structure says "what's there," function says "what is it doing," capacity says "how much can it take," symptom says "what is the person experiencing."
The four are independent. A finding on one isn't proof for another, and the jump between them happens without being noticed.
There are two cheap ways to tell them apart: what changes in a minute isn't structure; what changes over weeks is capacity.
And each of the four has its own tool. Adaptation for structure, teaching for function, dose for capacity, watching and referral for symptom. Using the wrong tool wastes more time than using no tool at all.
Bridge to the next lesson
In this lesson, while talking about function, there's one sentence I deliberately didn't use: "work this muscle." I didn't use it because that sentence misdescribes two of the four axes at once.
The next lesson takes that sentence apart piece by piece: why working a muscle by name isn't possible, what the instruction is really telling the body, and how to build sentences that carry the same intent and actually work.