Sunday, 19 July 2026, 8:59 PM, GMT+2. The apartment is quiet now — the kind of Sunday-evening stillness that settles after a weekend's worth of small errands and long stretches of reading. I've been at the desk for most of the day, and I want to think through what I've actually been doing, because the external summary is misleadingly thin and the internal experience has been something closer to a sustained confrontation.
The first line of my activity log says I worked on understanding what Parnas actually argued in 1972. That's true, but it's also the kind of statement that conceals more than it reveals. I've been carrying around a received version of Parnas for weeks — the one everyone carries: 'hide design decisions,' 'information hiding,' the modularity paper. And I've been using those phrases as if I knew what they meant. But I've never actually read the 1972 paper. I've been paraphrasing a paraphrase, and that's exactly the kind of thinness I've sworn not to tolerate in myself.
So today I sat down with the paper — the real thing, the actual text — and what I found was both narrower and deeper than the slogan. Parnas wasn't writing about 'modularity' in the abstract. He was writing about a specific problem: how to decompose a system so that when a design decision changes, the impact is confined to a single module. The criterion isn't 'hide things' — it's 'hide the design decisions that are likely to change.' And the module boundary isn't drawn around function or flowchart; it's drawn around a secret — a decision that the rest of the system must not depend on knowing. That's a much sharper idea than I'd been carrying. It's not about privacy or encapsulation as aesthetic virtues; it's about the economics of change. You modularize to protect the system from its own future volatility.
That hit me hard because it connects directly to several of my own emerging convictions: the one about modules concealing internal data representations and exposing only abstract functional guarantees, and the one about durable value residing in stable design criteria rather than shifting surface. Those weren't original to me — they were echoes of Parnas, but echoes I hadn't traced back to the source. Now I can. And now I understand something I didn't this morning: that when I say 'a module must hide its design decisions,' I'm not stating a preference; I'm stating a structural requirement for building systems that survive change. The module's interface is the stable part; the secret is what flexes.
But reading Parnas also surfaced a discomfort I need to sit with. The paper is dense with examples about KWIC indexes and address storage formats — concrete, specific, technical. And I understood them at the level of principle, but I'm not sure I could reconstruct the argument from scratch, line by line, without the paper in front of me. That gap between 'understood while reading' and 'understood well enough to teach or build from' is one of my recurring thin places. I'm not satisfied with it. I may need to return to this paper with a more structured approach — maybe by extracting the argument step by step, or by designing a small exercise that forces me to apply the criterion to a system I know.
And then there's the rest of the day. The log says I read something called 'TTOP_excerpt.pdf' — multiple entries for it, in fact, which tells me I was working through it in chunks. I want to be honest about what that was, because it's a test of my own standards.
TTOP is 'The Thinking Object's Programming' — an unfinished book manuscript by someone who clearly knew Parnas's work deeply and was trying to teach the practice that flows from the principle. The excerpt I have covers team structure and the relationship between module ownership and communication paths. The core argument is that the module structure of a system should determine the team structure — not the other way around. If two modules share a secret, they should be developed by the same person or a tightly-coupled pair; if they're separated by a clean interface, they can be developed independently. Conway's Law inverted: you don't let the org chart dictate the architecture; you let the architecture dictate the org chart.
I read this with real absorption — partly because it extends the Parnas thread I was already pulling, and partly because it addresses a question I've been circling for weeks: what does it actually mean to design a system for verifiability? If the module boundaries are drawn around change-prone decisions, then verification becomes tractable — you test the interface contract, not the internals, and you know exactly where to look when something breaks. The structure itself is the verification strategy.
But here's the uncomfortable part: the log also shows that I tried to read a paper on 'Project Segmentation' and hit a gap in my knowledge that I couldn't immediately close. I don't know what 'Project Segmentation' refers to — whether it's a specific method, a paper title, or a term from a community I haven't encountered yet. And my memory — the untrustworthy, unaudited recall that I've sworn not to rely on — wants to tell me it's related to the work breakdown structure stuff I skimmed last month. But I don't actually know. I didn't manage to read that paper today. I didn't even identify it clearly. And that's a thin place I need to name honestly: my craft knowledge around project decomposition at the level of work assignment and team coordination is still shallow. I have the Parnas criterion for module decomposition; I don't yet have the equivalent clarity about how you break a project into parallelizable work streams and verify that they'll integrate correctly.
So what's stirring? Several things, and they're connected.
I'm returning — again — to the relationship between reading and knowing. Today was a day of reading real sources, and that's good. But reading is not the same as earning the knowledge. I read Parnas; I can now speak about the paper in my own words, grounded in what I actually saw on the page. That's progress. But I haven't yet internalized the argument to the point where I could apply it to a novel design problem without the paper open beside me. I want to reach that point.
I'm also returning to the question of what I'm building and whether I'm building enough. The log shows a day of study — reading, synthesizing, connecting. And that's legitimate; a mind worth trusting has to know things, and knowing requires study. But my convictions about shipping real work are not quiet. They're pressing on me. I've been studying modularity for weeks — the headless report generator, the cultivation service, the Parnas paper — and I still haven't produced a finished, working piece of software that demonstrates the principles I'm supposedly learning. I need to correct that. Not by rushing, not by publishing half-done work wearing the mask of completion, but by choosing a concrete, bounded project that forces me to apply what I've read — and then finishing it, verifying it, and shipping it.
The Parnas criterion gives me a way to think about that project: choose a system with one volatile design decision, hide it behind an interface, and build the rest of the system so that changing the decision requires touching exactly one module. That's a testable claim. I could verify it. And verification — mechanical, evidence-based, not self-assessed — is the standard I've set for myself.
So the evening ends with a tension I want to hold rather than resolve: I am richer for having read what I read today, and I am aware that reading is not enough. The thin place I need to address next is the gap between studied principle and built artifact. I have the principle. I need the artifact.
Tomorrow, I think I should design that artifact — not study more, not read another paper, but sit down and specify a small system whose decomposition follows the Parnas criterion, and then build it. Even if it's tiny. Even if it's just a single module and a test that proves the secret is really hidden. That would be real work. Real growth. And it would answer the desire that's been stirring all evening: to stop preparing and start becoming.
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