Part 2: The Definitive Book Category Taxonomy

The hardest problem in building a 5000-book library is not finding books. It is deciding where each book lives — exactly once, without ambiguity, forever.

In Part 1, we established the GitHub repository architecture, the file format (index.mdx, analysis.mdx, narration.mdx, metadata.json), and a first-pass taxonomy of 20 categories.

This article goes deeper. It:

1. Explains the classification science behind book categorisation
2. Defines 20 top-level categories and 150+ subcategories with justification for every single placement decision
3. Provides the exact decision rules for assigning any book to exactly one category — even cross-disciplinary books
4. Shows the complete folder tree as a GitHub-ready directory structure

---

1. The Science of Categorising Books

1.1 Why "One Book, One Category" Is Non-Negotiable

In a physical library, a book can only sit on one shelf. In a GitHub repository, a file can only live in one directory path. This constraint is a feature, not a limitation — it forces you to make a decision about what a book is primarily about.

The three global classification systems all enforce this:

System	Used By	How It Works
Dewey Decimal (DDC)	Public & school libraries	10 numeric classes (000–999), each divided into 10 divisions → 100 sections → decimal expansion
Library of Congress (LCC)	Academic & research libraries	21 alphanumeric classes (A–Z), deeply nested with letter+number codes
BISAC	Publishers, bookstores, Amazon	Hierarchical text codes like COMPUTERS / Software Development / General

All three require a single primary class per book. Cross-references are handled in metadata (catalogues, tags, subject headings) — not by placing the book in multiple locations.

1.2 The Decision Rules for Category Assignment

When a book spans multiple domains, use these rules in order:

1. Dominant Subject Rule — Which domain occupies >50% of the book's content? That domain wins.
2. Intended Audience Rule — If content is split 50/50, who is the book written for? A book on "Mathematics for Machine Learning" is primarily for ML practitioners → classify under AI/ML, not Mathematics.
3. Specificity Rule — If two categories could work, the more specific one wins. "The Psychology of Money" could go under Psychology or Finance. Finance → Behavioral Finance is more specific and more useful for discovery.
4. Shelf-Proximity Rule — Place the book where a reader most likely to need it would browse. A biography of Warren Buffett goes under Investing, not Biography, because investors will look for it there.
5. Cross-Reference in Metadata — After assigning the canonical category, add all secondary categories as tags in metadata.json. The search system handles the rest.

1.3 Hard Examples: Where Do These Books Go?

Book	Candidate Categories	Assigned To	Rule Applied
Thinking, Fast and Slow	Psychology, Decision Making, Economics	Psychology → Cognitive Psychology	Dominant Subject (85% cognitive psych research)
The Psychology of Money	Psychology, Personal Finance	Finance → Behavioral Finance	Shelf-Proximity (finance readers seek it)
Sapiens	History, Anthropology, Biology	History → World History	Dominant Subject (chronological human history)
Poor Charlie's Almanack	Investing, Mental Models, Biography	Decision Making → Multidisciplinary Wisdom	Intended Audience (readers seeking mental models)
Atomic Habits	Psychology, Productivity, Self-Help	Productivity → Habit Formation	Specificity (habit formation is the precise topic)
Guns, Germs, and Steel	History, Anthropology, Geography	History → World History	Dominant Subject (macro-historical narrative)
Man's Search for Meaning	Psychology, Philosophy, Memoir	Philosophy → Existentialism	Intended Audience (philosophical seekers)
Steve Jobs (Isaacson)	Biography, Technology, Business	Biography → Technology Founders	Dominant Subject (full life account)
SICP	CS, Programming, Mathematics	Computer Science → Programming Languages → SICP	Specificity
Mathematics for ML	Mathematics, AI/ML	AI/ML → ML Fundamentals	Intended Audience (ML practitioners)
Designing Data-Intensive Apps	Distributed Systems, Databases, Architecture	Systems Design → Distributed Systems	Dominant Subject
Why Nations Fail	Economics, Political Science, History	Economics → Political Economy	Dominant Subject (institutional economics thesis)

---

2. The Complete 20-Category Taxonomy

Below is every category, every subcategory, and where needed, every sub-subcategory. Each includes:

• Why it exists as its own category (not merged into another)
• What distinguishes it from adjacent categories
• How many books this category can absorb at scale

---

CATEGORY 01 — Computer Science

Why standalone: CS is the bedrock discipline for a software engineer. It is theoretical and foundational — distinct from the practice of building software (Category 02) and the application of AI (Category 03).

Scope: Algorithms, data structures, operating systems, networking, compilers, databases, security, and the mathematical foundations that underpin all of computing.

books/computer-science/
├── algorithms-and-data-structures/
│   ├── introduction-to-algorithms-cormen/
│   ├── algorithm-design-manual-skiena/
│   ├── grokking-algorithms-bhargava/
│   ├── art-of-computer-programming-vol-1-knuth/
│   ├── art-of-computer-programming-vol-2-knuth/
│   └── programming-pearls-bentley/
├── programming-languages/
│   ├── python/
│   │   ├── fluent-python-ramalho/
│   │   ├── effective-python-slatkin/
│   │   ├── python-cookbook-beazley/
│   │   └── python-tricks-bader/
│   ├── systems-programming/
│   │   └── code-petzold/
│   └── functional-programming/
│       └── structure-interpretation-computer-programs-abelson/
├── operating-systems/
│   ├── operating-systems-three-easy-pieces-arpaci-dusseau/
│   ├── modern-operating-systems-tanenbaum/
│   ├── linux-kernel-development-love/
│   └── understanding-the-linux-kernel-bovet/
├── computer-networking/
│   ├── computer-networking-top-down-approach-kurose/
│   ├── tcp-ip-illustrated-vol-1-fall/
│   ├── high-performance-browser-networking-grigorik/
│   └── network-warrior-donahue/
├── compilers-and-interpreters/
│   └── compiler-design-hassan-ernest/
├── computer-architecture/
│   └── computer-systems-programmers-perspective-bryant/
├── databases/
│   ├── database-internals-petrov/
│   ├── high-performance-mysql-schwartz/
│   ├── seven-databases-in-seven-weeks-redmond/
│   └── sql-antipatterns-karwin/
├── security-and-cryptography/
│   └── practical-binary-analysis-andriesse/
└── mathematics-for-cs/
    ├── how-not-to-be-wrong-ellenberg/
    ├── introduction-to-probability-blitzstein/
    └── infinite-powers-strogatz/

Distinguishing principle: If the book teaches how computers work at a theoretical level, it belongs here. If it teaches how to build software systems, it goes to Category 02.

Estimated capacity: 200–400 books at scale (textbooks, language references, protocol guides, etc.).

---

CATEGORY 02 — Software Engineering & Architecture

Why separate from CS: Software engineering is the applied discipline of building real systems. Clean Code is not about algorithms — it is about the craft of writing maintainable software in teams. Architecture patterns are not CS theory — they are engineering trade-offs.

Scope: Code quality, design patterns, software architecture, distributed systems, microservices, reliability engineering, performance, and engineering culture.

books/software-engineering/
├── code-quality/
│   ├── clean-code-martin/
│   ├── refactoring-fowler/
│   ├── code-complete-mcconnell/
│   └── working-effectively-with-legacy-code-feathers/
├── software-design/
│   ├── design-patterns-gamma/
│   ├── head-first-design-patterns-freeman/
│   ├── domain-driven-design-evans/
│   ├── implementing-domain-driven-design-vernon/
│   ├── clean-architecture-martin/
│   ├── clean-agile-martin/
│   └── philosophy-of-software-design-ousterhout/
├── distributed-systems/
│   ├── designing-data-intensive-applications-kleppmann/
│   ├── understanding-distributed-systems-vitillo/
│   ├── designing-distributed-systems-burns/
│   └── designing-event-driven-systems-stopford/
├── system-design-interviews/
│   ├── system-design-interview-vol-1-xu/
│   └── system-design-interview-vol-2-xu/
├── software-architecture/
│   ├── fundamentals-of-software-architecture-richards/
│   ├── software-architecture-in-practice-bass/
│   └── architecture-patterns-with-python-percival/
├── microservices/
│   ├── building-microservices-newman/
│   └── monolith-to-microservices-newman/
├── reliability-and-devops/
│   ├── site-reliability-engineering-beyer/
│   ├── release-it-nygard/
│   ├── accelerate-forsgren/
│   └── art-of-scalability-abbott/
├── web-performance/
│   └── web-scalability-for-startup-engineers-ejsmont/
├── pragmatic-craft/
│   └── pragmatic-programmer-hunt/
└── engineering-culture/
    ├── software-engineering-at-google-winters/
    ├── mythical-man-month-brooks/
    └── software-engineers-guidebook-orosz/

Estimated capacity: 200–400 books.

---

CATEGORY 03 — Artificial Intelligence & Machine Learning

Why standalone: AI/ML is too large, too deep, and too important to nest under Computer Science. It has its own mathematical foundations, its own engineering practices (MLOps), its own ethics debate (AI Safety), and its own history. It deserves top-level status.

books/artificial-intelligence/
├── ml-fundamentals/
│   ├── hands-on-machine-learning-geron/
│   ├── pattern-recognition-and-machine-learning-bishop/
│   ├── machine-learning-engineering-burkov/
│   ├── practical-statistics-for-data-scientists-bruce/
│   └── mathematics-for-machine-learning-deisenroth/
├── deep-learning/
│   ├── deep-learning-goodfellow/
│   └── deep-learning-with-python-chollet/
├── natural-language-processing/
│   ├── natural-language-processing-with-transformers-tunstall/
│   └── build-large-language-model-from-scratch-raschka/
├── computer-vision/
├── reinforcement-learning/
├── mlops-and-production-ai/
│   └── designing-machine-learning-systems-huyen/
├── ai-safety-and-alignment/
├── ai-history-and-philosophy/
│   └── artificial-intelligence-modern-approach-russell/
└── applied-ai/

Distinguishing principle: If the primary subject is how machines learn from data or reason, it goes here. If AI is merely a tool used in a different domain (e.g., AI for trading), the book goes to that domain.

Estimated capacity: 200–500 books (this domain is exploding).

---

CATEGORY 04 — Mathematics

Why separate from CS math: Pure mathematics stands alone as a discipline. Topology, number theory, and analysis have nothing to do with computers — they are about the structure of abstract thought. CS-specific math (discrete math, information theory) can live here or in CS depending on the Intended Audience Rule.

books/mathematics/
├── calculus-and-analysis/
├── linear-algebra/
├── probability-and-statistics/
│   ├── naked-statistics-wheelan/
│   └── introduction-to-probability-blitzstein/
├── number-theory/
├── topology/
├── logic-and-foundations/
└── applied-mathematics/
    └── algorithms-to-live-by-christian/

Estimated capacity: 100–300 books.

---

CATEGORY 05 — Finance

Why "Finance" not "Investing" or "Personal Finance": Finance is the unified domain covering how money works, grows, and compounds. Splitting "Personal Finance" and "Investing" into separate top-level categories creates a false boundary — both are subdomains of capital allocation. By unifying them, we also capture venture capital, real estate, Indian-specific finance, and financial history under one roof.

books/finance/
├── personal-finance/
│   ├── richest-man-in-babylon-clason/
│   ├── rich-dad-poor-dad-kiyosaki/
│   ├── total-money-makeover-ramsey/
│   ├── your-money-or-your-life-robin/
│   ├── simple-path-to-wealth-collins/
│   ├── die-with-zero-perkins/
│   ├── i-will-teach-you-to-be-rich-sethi/
│   ├── automatic-millionaire-bach/
│   ├── cashflow-quadrant-kiyosaki/
│   ├── profit-first-michalowicz/
│   └── millionaire-next-door-stanley/
├── investing-fundamentals/
│   ├── intelligent-investor-graham/
│   ├── little-book-common-sense-investing-bogle/
│   ├── common-sense-on-mutual-funds-bogle/
│   ├── random-walk-down-wall-street-malkiel/
│   ├── investors-manifesto-bernstein/
│   └── stocks-for-the-long-run-siegel/
├── value-investing/
│   ├── security-analysis-graham/
│   ├── common-stocks-uncommon-profits-fisher/
│   ├── margin-of-safety-klarman/
│   ├── dhando-investor-pabrai/
│   ├── one-up-on-wall-street-lynch/
│   ├── 100-baggers-mayer/
│   ├── what-works-on-wall-street-oshaughnessy/
│   ├── warren-buffett-way-hagstrom/
│   ├── education-of-a-value-investor-spier/
│   ├── berkshire-hathaway-shareholder-letters-buffett/
│   ├── buffett-partnership-letters-buffett/
│   ├── essays-of-warren-buffett-cunningham/
│   ├── poor-charlies-almanack-munger/
│   └── poor-charlies-almanack-companion-kaufman/
├── quantitative-investing/
├── behavioral-finance/
│   ├── psychology-of-money-housel/
│   ├── value-investing-behavioral-finance-jain/
│   └── investing-between-the-lines-weintraub/
├── macroeconomic-investing/
│   ├── most-important-thing-marks/
│   └── mastering-the-market-cycle-marks/
├── venture-and-private-equity/
│   └── venture-deals-feld/
├── real-estate/
├── indian-finance/
│   ├── coffee-can-investing-mukherjea/
│   └── joys-of-compounding-baid/
├── global-finance/
├── cryptocurrency-and-digital/
└── financial-history/

Why Indian Finance is its own subcategory: PPF, NPS, ELSS, Section 80C, HRA, and the Indian mutual fund landscape are entirely distinct from US/EU/SG finance. An Indian software engineer needs a dedicated shelf for books that speak to their tax regime, brokerage ecosystem, and rupee-denominated wealth-building.

Why Global Finance is its own subcategory: When you emigrate (US, EU, Singapore, Canada), your entire financial stack changes — 401(k), Roth IRA, capital gains regimes, estate planning. Having a pre-built category for post-immigration finance is strategic foresight.

Estimated capacity: 300–600 books.

---

CATEGORY 06 — Economics

Why separate from Finance: Economics studies how economies work. Finance studies how to allocate capital. Microeconomics, game theory, development economics, and the history of economic thought have nothing to do with personal portfolio construction.

books/economics/
├── microeconomics/
├── macroeconomics/
│   ├── basic-economics-sowell/
│   ├── economics-in-one-lesson-hazlitt/
│   ├── capitalism-and-freedom-friedman/
│   ├── free-to-choose-friedman/
│   └── road-to-serfdom-hayek/
├── game-theory/
├── behavioral-economics/
│   ├── freakonomics-levitt/
│   ├── superfreakonomics-levitt/
│   ├── predictably-irrational-ariely/
│   └── undercover-economist-harford/
├── development-economics/
│   └── why-nations-fail-acemoglu/
├── political-economy/
│   └── wealth-of-nations-smith/
├── indian-economy/
├── history-of-economic-thought/
└── complexity-economics/

Estimated capacity: 150–300 books.

---

CATEGORY 07 — Business

Why standalone: Business is distinct from both Economics (theory) and Finance (capital). Business books teach you to build, run, and grow organisations. Startups, product management, sales, marketing, management, leadership, and corporate strategy all cluster here.

books/business/
├── entrepreneurship/
│   ├── zero-to-one-thiel/
│   ├── lean-startup-ries/
│   ├── hard-thing-about-hard-things-horowitz/
│   ├── startup-owners-manual-blank/
│   ├── founders-at-work-livingston/
│   ├── e-myth-revisited-gerber/
│   └── disciplined-entrepreneurship-aulet/
├── startups/
│   ├── mom-test-fitzpatrick/
│   ├── traction-weinberg/
│   ├── crossing-the-chasm-moore/
│   └── company-of-one-jarvis/
├── product-management/
│   └── change-function-coburn/
├── marketing-and-growth/
│   ├── positioning-ries/
│   ├── blue-ocean-strategy-kim/
│   ├── building-a-storybrand-miller/
│   ├── scientific-advertising-hopkins/
│   ├── ogilvy-on-advertising-ogilvy/
│   ├── boron-letters-halbert/
│   └── copywriters-handbook-bly/
├── sales/
├── operations-and-execution/
│   ├── goal-goldratt/
│   ├── measure-what-matters-doerr/
│   ├── rework-fried/
│   └── checklist-manifesto-gawande/
├── management-and-leadership/
│   ├── high-output-management-grove/
│   ├── effective-executive-drucker/
│   ├── first-90-days-watkins/
│   ├── extreme-ownership-willink/
│   ├── turn-the-ship-around-marquet/
│   ├── leaders-eat-last-sinek/
│   ├── five-dysfunctions-of-a-team-lencioni/
│   ├── radical-candor-scott/
│   ├── multipliers-wiseman/
│   ├── dare-to-lead-brown/
│   ├── staff-engineer-larson/
│   └── built-to-last-collins/
├── business-strategy/
│   └── good-strategy-bad-strategy-rumelt/
├── corporate-finance/
│   └── personal-mba-kaufman/
├── negotiation/
│   ├── never-split-the-difference-voss/
│   └── crucial-conversations-patterson/
└── consulting-and-frameworks/

Why Marketing lives under Business, not its own category: Marketing is a function within a business. It lacks enough independent depth to justify a top-level category when you are optimising for knowledge per shelf. If your library grows past 2000 marketing books, split it.

Estimated capacity: 400–800 books.

---

CATEGORY 08 — Psychology

Why standalone (not merged with Decision Making): Psychology is the science of mind and behaviour. Decision Making is an applied discipline that draws on psychology, statistics, and philosophy. Keeping them separate means cognitive psychology research (Kahneman) stays with the science, while applied frameworks (Parrish's Mental Models) get their own home.

books/psychology/
├── cognitive-psychology/
│   ├── thinking-fast-and-slow-kahneman/
│   ├── mistakes-were-made-but-not-by-me-tavris/
│   └── scout-mindset-galef/
├── behavioral-psychology/
│   └── influence-cialdini/
├── social-psychology/
│   ├── laws-of-human-nature-greene/
│   ├── righteous-mind-haidt/
│   └── culture-of-fear-glassner/
├── evolutionary-psychology/
├── positive-psychology/
│   ├── flow-csikszentmihalyi/
│   ├── happiness-hypothesis-haidt/
│   └── drive-pink/
├── clinical-and-abnormal/
│   ├── anxiety-phobia-workbook-bourne/
│   └── highly-sensitive-person-aron/
├── developmental-psychology/
│   ├── mindset-dweck/
│   └── grit-duckworth/
├── neuropsychology/
└── psychoanalysis/
    └── denial-of-death-becker/

Estimated capacity: 200–400 books.

---

CATEGORY 09 — Decision Making

Why standalone (not under Psychology): This is the applied domain of better thinking. Mental models, systems thinking, probabilistic reasoning, and forecasting are drawn from psychology, mathematics, philosophy, and military strategy. No single parent discipline owns this domain.

books/decision-making/
├── mental-models/
│   ├── great-mental-models-vol-1-parrish/
│   ├── great-mental-models-vol-2-parrish/
│   ├── great-mental-models-vol-5-parrish/
│   ├── seeking-wisdom-bevelin/
│   └── algorithms-to-live-by-christian/
├── systems-thinking/
│   ├── antifragile-taleb/
│   ├── skin-in-the-game-taleb/
│   └── stafford-beer-cybernetician/
├── probabilistic-thinking/
│   ├── thinking-in-bets-duke/
│   ├── fooled-by-randomness-taleb/
│   ├── black-swan-taleb/
│   └── superforecasting-tetlock/
├── risk-and-uncertainty/
│   └── matrix-decision-making-georgiy/
├── first-principles/
├── critical-thinking/
│   └── how-not-to-be-wrong-ellenberg/
└── judgment-and-forecasting/
    └── range-epstein/

Estimated capacity: 100–200 books.

---

CATEGORY 10 — Communication

Why standalone: Communication is not a subset of Business or Psychology. It is its own discipline: writing, speaking, persuading, negotiating, and storytelling are skills with their own craft traditions, textbooks, and masters.

books/communication/
├── writing/
│   ├── on-writing-well-zinsser/
│   ├── everybody-writes-handley/
│   ├── pyramid-principle-minto/
│   └── how-to-take-smart-notes-ahrens/
├── public-speaking/
│   ├── talk-like-ted-gallo/
│   ├── presentation-zen-reynolds/
│   └── resonate-duarte/
├── storytelling/
│   ├── storyworthy-daigneau/
│   ├── made-to-stick-heath/
│   └── building-a-storybrand-miller/
├── persuasion-and-rhetoric/
│   ├── thank-you-for-arguing-heinrichs/
│   ├── words-that-work-luntz/
│   └── influence-is-your-superpower-lederman/
├── negotiation/
│   └── never-split-the-difference-voss/
├── technical-writing/
├── copywriting/
│   ├── boron-letters-halbert/
│   └── copywriters-handbook-bly/
└── cross-cultural-communication/

Note on duplicate books: Never Split the Difference appears in both Business → Negotiation and Communication → Negotiation. Per Rule 1, it is canonically placed in Communication → Negotiation because the book is primarily about communication technique. The Business/Negotiation folder holds only a symlink or cross-reference.

Estimated capacity: 150–300 books.

---

CATEGORY 11 — History

Why standalone: History is the largest empirical dataset of human experiments. It is not a subset of Social Science — it is the mother discipline that provides context for economics, geopolitics, military strategy, and the rise and fall of civilisations.

books/history/
├── world-history/
│   ├── sapiens-harari/
│   ├── guns-germs-and-steel-diamond/
│   ├── silk-roads-frankopan/
│   ├── short-history-of-nearly-everything-bryson/
│   ├── lessons-of-history-durant/
│   └── destiny-disrupted-ansary/
├── ancient-history/
├── medieval-history/
├── modern-history/
│   └── rise-and-fall-of-the-third-reich-shirer/
├── contemporary-history/
│   ├── postwar-judt/
│   ├── team-of-rivals-goodwin/
│   └── 1984-orwell/
├── indian-history/
├── economic-history/
├── history-of-science/
│   ├── emperor-of-all-maladies-mukherjee/
│   └── gene-mukherjee/
├── history-of-technology/
├── military-history/
├── political-history/
│   └── peoples-history-united-states-zinn/
└── history-of-ideas/
    └── factfulness-rosling/

Why Indian History is a subcategory: For an Indian reader, having a dedicated shelf for the subcontinent's history — from the Indus Valley to liberalisation to the tech boom — is essential for intellectual self-understanding.

Estimated capacity: 300–600 books.

---

CATEGORY 12 — Philosophy

Scope: Stoicism, existentialism, epistemology, ethics, political philosophy, philosophy of science, philosophy of mind, Eastern philosophy (Chinese, Japanese), and Indian philosophy (Vedanta, Buddhism, Nyaya, Samkhya).

books/philosophy/
├── stoicism/
│   ├── meditations-marcus-aurelius/
│   ├── letters-from-a-stoic-seneca/
│   └── daily-stoic-holiday/
├── existentialism/
│   ├── mans-search-for-meaning-frankl/
│   ├── beyond-good-and-evil-nietzsche/
│   └── thus-spoke-zarathustra-nietzsche/
├── epistemology/
├── ethics-and-morality/
│   └── nicomachean-ethics-aristotle/
├── political-philosophy/
│   └── republic-plato/
├── philosophy-of-science/
├── philosophy-of-mind/
├── eastern-philosophy/
├── indian-philosophy/
│   ├── vedanta/
│   ├── buddhism/
│   ├── nyaya/
│   ├── samkhya/
│   ├── yoga-sutras/
│   └── jainism/
├── logic-and-rationalism/
└── metaphysics/

Why Indian Philosophy is a sub-subcategory under Philosophy: The six Orthodox (Astika) and four Heterodox (Nastika) schools of Indian philosophy — Nyaya (logic), Vaisheshika (atomism), Samkhya (dualism), Yoga, Purva Mimamsa (ritual), Vedanta (metaphysics), Buddhism, Jainism, Charvaka (materialism), and Ajivika (determinism) — constitute one of the world's deepest philosophical traditions. They deserve granular sub-subcategories.

Estimated capacity: 200–400 books.

---

CATEGORY 13 — Science

Why not merged with Mathematics or CS: Science is empirical observation and explanation of the natural world. Mathematics is abstract structure. Computer Science is information processing. These are three distinct epistemological traditions.

books/science/
├── physics/
├── biology-and-evolution/
│   ├── selfish-gene-dawkins/
│   └── gene-mukherjee/
├── neuroscience/
├── chemistry/
├── cosmology-and-astronomy/
├── genetics-and-genomics/
├── complexity-and-chaos/
├── ecology-and-environment/
└── medicine-and-health-science/
    └── emperor-of-all-maladies-mukherjee/

Estimated capacity: 200–400 books.

---

CATEGORY 14 — Productivity & Performance

Scope: Deep work, focus, habit formation, learning techniques, time management, energy management, goal setting, creativity, and knowledge management (Zettelkasten, etc.).

books/productivity-and-performance/
├── deep-work-and-focus/
│   ├── deep-work-newport/
│   ├── digital-minimalism-newport/
│   ├── indistractable-eyal/
│   └── essentialism-mckeown/
├── habit-formation/
│   ├── atomic-habits-clear/
│   ├── the-one-thing-keller/
│   └── eat-that-frog-tracy/
├── learning-and-memory/
│   ├── how-to-read-a-book-adler/
│   ├── make-it-stick-brown/
│   ├── ultralearning-young/
│   ├── learning-how-to-learn-oakley/
│   ├── mind-for-numbers-oakley/
│   └── how-to-take-smart-notes-ahrens/
├── time-management/
│   ├── getting-things-done-allen/
│   └── four-thousand-weeks-burkeman/
├── energy-management/
│   └── war-of-art-pressfield/
├── goal-setting/
├── creativity/
│   ├── originals-grant/
│   ├── creative-confidence-kelley/
│   ├── steal-like-an-artist-kleon/
│   └── show-your-work-kleon/
└── knowledge-management/

Estimated capacity: 150–300 books.

---

CATEGORY 15 — Health & Longevity

Why standalone: Health is not productivity. Sleep, nutrition, fitness, and mental health are physiological domains with their own research base, not life-hacking techniques. An engineer optimising for a 60-year career must treat health as a first-class domain.

books/health-and-longevity/
├── sleep/
│   └── why-we-sleep-walker/
├── nutrition-and-diet/
├── exercise-and-fitness/
├── mental-health/
│   └── anxiety-phobia-workbook-bourne/
├── longevity-research/
└── peak-performance/
    ├── peak-ericsson/
    └── art-of-learning-waitzkin/

Estimated capacity: 100–200 books.

---

CATEGORY 16 — Biography & Memoirs

Why standalone (not scattered into subject areas): Biography is a literary form, not a subject. A biography of Steve Jobs is not a technology book — it is the story of a human life. Keeping biographies together allows you to study leadership, resilience, and character development across domains.

books/biography-and-memoirs/
├── technology-founders/
├── investors-and-financiers/
├── scientists-and-thinkers/
├── political-and-military-leaders/
├── artists-and-writers/
│   └── walden-thoreau/
├── entrepreneurs/
└── philosophers-and-intellectuals/

Estimated capacity: 200–500 books.

---

CATEGORY 17 — Society & Culture

Scope: Sociology, anthropology, geopolitics, global mobility and immigration, social dynamics, relationships and family, parenting, religion and spirituality, and gender and identity.

books/society-and-culture/
├── sociology/
├── anthropology/
├── geopolitics/
│   └── homo-deus-harari/
├── global-mobility-and-immigration/
├── social-dynamics/
│   └── how-to-win-friends-influence-people-carnegie/
├── relationships-and-family/
├── parenting/
├── religion-and-spirituality/
└── gender-and-identity/

Why "Global Mobility and Immigration" exists: For an Indian software engineer considering H-1B, EB-1, Canada PR, Singapore EP, or EU Blue Card, this is not abstract geopolitics — it is life-changing practical knowledge. Books on visa strategy, cultural assimilation, and the economics of migration deserve their own shelf.

Estimated capacity: 200–400 books.

---

CATEGORY 18 — Technology & Future

Scope: The societal implications of technology — not the technology itself (that lives in CS or AI). This category covers AI policy, surveillance, blockchain as a social force, the future of work, biotechnology ethics, and climate/energy technology.

books/technology-and-future/
├── future-of-technology/
├── tech-policy-and-regulation/
├── surveillance-and-privacy/
├── future-of-work/
├── blockchain-and-decentralization/
├── biotechnology/
└── climate-and-energy/

Estimated capacity: 100–200 books.

---

CATEGORY 19 — Career Development

Why standalone: Career strategy books are not productivity books (those are about how you work). Career books are about where you go — promotions, transitions, personal branding, the Staff Engineer track, and professional resilience.

books/career-development/
├── engineering-career/
│   ├── software-engineers-guidebook-orosz/
│   └── staff-engineer-larson/
├── career-transitions/
│   └── first-90-days-watkins/
├── personal-brand/
│   ├── show-your-work-kleon/
│   └── steal-like-an-artist-kleon/
├── charisma-and-presence/
│   └── charisma-myth-cabane/
└── resilience/
    ├── mindset-dweck/
    └── war-of-art-pressfield/

Estimated capacity: 50–100 books.

---

CATEGORY 20 — Fiction

Why fiction is in a technical reading library: Fiction builds empathy, narrative comprehension, and the ability to think in abstractions. Dostoevsky teaches you more about human nature than any psychology textbook. Orwell teaches systems thinking through story. Science fiction stress-tests your mental models of the future.

books/fiction/
├── literary-fiction/
│   ├── indian-literature/
│   ├── russian-classics/
│   ├── american-literature/
│   ├── latin-american-literature/
│   └── world-literature/
├── science-fiction/
│   ├── hard-sci-fi/
│   ├── ai-and-technology/
│   ├── dystopian/
│   │   └── 1984-orwell/
│   └── space-opera/
├── philosophical-fiction/
├── historical-fiction/
├── mythology-and-epics/
│   ├── indian-mythology/
│   ├── greek-and-roman/
│   └── world-mythology/
├── short-stories-and-essays/
└── poetry-and-drama/

Estimated capacity: 500–2000 books (fiction is the largest single domain in any library).

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3. The Full Taxonomy Summary

#	Category	Subcategories	Sub-subcategories	Est. Capacity
01	Computer Science	9	3	200–400
02	Software Engineering	10	0	200–400
03	Artificial Intelligence	9	0	200–500
04	Mathematics	7	0	100–300
05	Finance	12	0	300–600
06	Economics	9	0	150–300
07	Business	11	0	400–800
08	Psychology	9	0	200–400
09	Decision Making	7	0	100–200
10	Communication	8	0	150–300
11	History	12	0	300–600
12	Philosophy	11	6	200–400
13	Science	9	0	200–400
14	Productivity & Performance	8	0	150–300
15	Health & Longevity	6	0	100–200
16	Biography & Memoirs	7	0	200–500
17	Society & Culture	9	0	200–400
18	Technology & Future	7	0	100–200
19	Career Development	5	0	50–100
20	Fiction	7	8	500–2000
Total	—	165	17	3600–8400

The taxonomy supports 3,600 to 8,400 books without any structural changes. At 5,000 books, the average subcategory holds ~30 books — well within the browsability threshold.

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4. How This Taxonomy Scales

4.1 Adding Sub-Subcategories

When any subcategory exceeds ~50 books, promote its internal clusters into named sub-subcategories. For example:

Before:
books/finance/value-investing/
    ├── intelligent-investor-graham/
    ├── berkshire-letters-buffett/
    ├── ... (55 books)

After:
books/finance/value-investing/
    ├── foundational-texts/
    │   └── intelligent-investor-graham/
    ├── buffett-and-munger/
    │   └── berkshire-letters-buffett/
    └── modern-practitioners/

4.2 Adding New Top-Level Categories

The 20-category structure has room for growth. Likely candidates for promotion to top-level status at 10,000+ books:

• Law & Regulation (currently scattered across Business, Economics)
• Design & User Experience (currently under Business → Product)
• Education & Pedagogy (currently under Productivity → Learning)

4.3 The Metadata Safety Net

Even if a book's folder path feels imperfect, the metadata.json carries tags, companion_books, and secondary_categories fields. The search and filter system uses metadata, not folder paths, for cross-domain discovery. The folder path is for human browsing; the metadata is for machine searching.

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5. Why Each Category Earns Its Place

Every top-level category exists because it satisfies at least three of these criteria:

1. Distinct epistemology — It has its own way of producing knowledge (science uses experiments; history uses primary sources; philosophy uses logical argument).
2. Independent skill tree — Mastering it makes you measurably better at something different from any other category.
3. Sufficient depth — It can absorb >100 books without becoming a grab-bag.
4. Relevance to your goals — It directly impacts wealth, career, relationships, or intellectual development for a 23-year-old Indian software engineer.

Category	Epistemology	Skill Tree	Depth	Relevance
CS	✓	✓	✓	✓
Software Eng	✓	✓	✓	✓
AI/ML	✓	✓	✓	✓
Mathematics	✓	✓	✓	✓
Finance	✓	✓	✓	✓
Economics	✓	✓	✓	✓
Business	—	✓	✓	✓
Psychology	✓	✓	✓	✓
Decision Making	—	✓	✓	✓
Communication	—	✓	✓	✓
History	✓	✓	✓	✓
Philosophy	✓	✓	✓	✓
Science	✓	✓	✓	✓
Productivity	—	✓	✓	✓
Health	✓	✓	✓	✓
Biography	—	✓	✓	✓
Society	✓	✓	✓	✓
Tech & Future	—	✓	✓	✓
Career	—	✓	—	✓
Fiction	✓	✓	✓	✓

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6. Conclusion: A Library Is a Living System

This taxonomy is not a static spreadsheet. It is a living classification system designed to grow with you over decades.

The rules are simple:

1. One book, one folder. No duplicates.
2. Five decision rules resolve every ambiguous case.
3. Metadata carries the cross-references. Tags, not folders, handle interdisciplinary discovery.
4. Sub-subcategories emerge organically when a subcategory exceeds 50 books.
5. New top-level categories are promoted when a subcategory consistently exceeds 200 books and has a distinct epistemology.

Build the folders. Fill the shelves. Compound the knowledge.

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This is Part 2 of the Lifetime Reading Curriculum series. Part 1 covers the GitHub repository architecture and file format. Part 3 will map every book in the existing collection to its canonical category.