The Dewey Decimal System
Unlock the secret map hidden on library shelves. Learn how to decode call numbers, predict where subjects live, and browse the stacks to discover books you didn't know you were looking for.
Like Duolingo, but for The Dewey Decimal System. Tomo turns the whole topic into a game you play five minutes a day, until it actually sticks.
A short one: 11 levels across 2 sections, about 22 minutes end to end, roughly 4 days at five minutes a day. It moves through Finding Any Book in the Stacks and Decoding the Neighborhood. It starts from scratch.
Free forever · No credit card · iPhone & Android
Key ideas in The Dewey Decimal System
- Dewey call numbers act like street addresses leading from broad topic to specific item
- The top line of a Dewey call number groups books by specific subject
- The line underneath the Dewey number identifies the specific author or title
- Numbers before the decimal point are sorted as standard whole numbers
- Digits after the decimal point are sorted digit-by-digit rather than as whole numbers (so .13 comes before .2)
- A shorter decimal comes before a longer decimal with a higher first digit
- When books share the same Dewey subject number, the lower line breaks the tie
- The letter and numbers below the Dewey number represent the author's last name
- Books on the same topic are alphabetized by author using this lower line
- Shelves read like a newspaper column: left to right on one shelf, then down to the next shelf in that same bookcase unit
- You only move to the next vertical bookcase section once you reach the bottom shelf of the current unit
- The Dewey decimal numbers are primarily reserved for non-fiction subjects
- Most public libraries pull fiction novels out of the standard Dewey 800s section
- Fiction is typically organized in its own separate section alphabetically by the author's last name
- Dewey organizes all knowledge into exactly ten master categories
- Every master category starts with a distinct hundred (000, 100, up to 900)
You've tried the other tabs
Thirty open tabs. Four facts you actually kept.
You watched. You nodded. By Sunday it was gone.
One answer, then back to scrolling.
Eight weeks. You meant to finish. You didn't.
Tomo gives The Dewey Decimal System the Duolingo treatment: levels, streaks, and quick quizzes that test what you just learned. That game loop is what the tabs above never had, so it's the one you actually finish.
Here's what playing it feels like
A real question from this course. Take your best guess.
What does the top line of a Dewey call number tell you about the book?
Get it right to open this lesson and 10 more in the app.
Where The Dewey Decimal System takes you
- 1
Finding Any Book in the Stacks
- Reading Call Numbers as Shelf Coordinates
- The Ten Master Classes of Knowledge
- 2
Decoding the Neighborhood
- Zooming In with Decimal Points
- Browsing Beyond the Search Bar
2 sections · 4 units · 11 levels. Built to play, not to enroll.
Tomo is in ChatGPT
Tomo is also a ChatGPT plugin: the same playable courses, built and played inside your chat.
Add Tomo to ChatGPT- What to ask
- “Make me a Tomo course on black holes.” “Turn this chat into a Tomo course.”
- What you get
- Quick questions with instant feedback, hearts and stars, ready to play in about a minute.
- Where it goes
- No sign-up to start. Connect your Tomo account and your streak carries on in the app.
You pick the voice
The Dewey Decimal System is taught in the Explain Like I'm 5 style: no big words. promise.. Want a different feel? In the app you can spin up the same topic in any of Tomo's teaching styles. Same facts, totally different vibe.
More History on Tomo
How Global Politics Works
Learn how power really flows between nations and why countries make the strategic choices they do. Decode foreign news headlines, understand treaties and alliances, and see through the theater of international relations.
Thinking Like a Historian
Move beyond memorizing dates and discover how history is actually made. Learn to interrogate biased sources, read archival silences, and dismantle the illusion of inevitability.
The Pickelhaube: Anatomy and Eclipse
Examine the craftsmanship, military logic, and tactical reality behind Europe's most recognizable spiked helmet. Discover how an aristocratic 19th-century status symbol evolved across imperial armies before shattering against the brutal realities of industrial warfare.
Secrets of the Pharaohs and Pyramids
Step into the sandals of an explorer to uncover how the pyramids were built and what life was like for the powerful kings and queens of the Nile. Master the mysteries of the desert and learn to read the stories left behind in stone.
Cave Art of the Dordogne
Explore the Ice Age masterworks of France's Vézère Valley. Learn to read how Paleolithic artists transformed subterranean limestone through optical illusions, mineral pyrotechnology, and deliberate spatial architecture.
Ancient Egypt: Life, Death, and Power
Look past the sand and gold to discover how ancient Egyptians actually lived, worked, and saw their cosmos. Learn to decode tomb paintings, understand the mechanics of mummification and pyramid construction, and trace the three-thousand-year rise and fall of the Nile's legendary rulers.
Start The Dewey Decimal System today.
Download Tomo, search The Dewey Decimal System, and play your first lesson in under a minute.