NOTE: Both Michelle Howard, the author of this informative post, and Liz Cottrill and Emily Kiser of Living Books Library in Tennessee highly recommend using the Dewey Decimal System to classify and organize your books. You can use LibraryThing or Michelle’s library database or this OCLC site to find the most commonly used call number in the Dewey Decimal System for any given book.

From Michelle Howard of Children’s Preservation Library in Michigan and Living Learning Libraries in Florida:

Indeed, the numbers to the right of the decimal shouldn’t be seen as any more intimidating than those on the left. They are only more specific. But, it is that very specificity that gets you where you want to go!
Let’s go back to our telephone number metaphor. If you were meeting a new friend, and she said, “My phone number is 228-5555,” you wouldn’t tell her to halt mid-way through, saying, “I can only handle the digits to the left of the dash,” because that would only get your call to her town, not to her house. So, maybe we should think of the numbers to the right of the decimal as those that actually get us to “the final destination;” thus they are not a burden, but are our most treasured tool.
Do you remember that we watched Mr. MELVIL Dewey (not the dastardly John) take “knowledge” and divide it by tens into the 000s, 100s, 200s, 300s, 400s, 500s, etc.? Then we saw that he took the 500s, for example, and divided them by tens again:

500s General
510s Math
520s Astronomy
530s Physics
540s Chemistry
550s Earth Sciences
560s….etc.

Well, we know that the pattern continues. For example, Dewey broke the 530s down by ten again, to highlight the main 10 aspects of Physics….bringing us to this:

530 General physics
531 Mechanics (here are your books about simple machines, such as the lever)
532 Fluids
533 Gases
534 Sound
535 Light
536 Heat
537 Electricity
538 Magnetism
539 Modern physics (quarks, etc.)

That all makes sense, right? Even if you couldn’t remember whether “Sound” was 534 or 535, it wouldn’t really matter, because you would know it is a pure science, and would thus start walking toward the 500s. While your patron is chatting, you dig into your memory (or look at your charts) and recall that the 530s are Physics. You’ve already nailed it down to a shelf or two, and it won’t be hard to spot the “Sound” books because they’ll all be together (thanks to the labels your database has printed out). If you eventually remember (or look at your chart) and see that “Sound” is 534, super! But either way, you’re very close.

If you even put all “Sounds” books at 534, and labeled with no additional detail, you’d be okay. But, if you use the more specific numbers, you get an even more refined collection, and thus can really narrow in on topics for kids hungry to learn. That is where the next set of numbers comes in.

If we are still using 534 as our example, Dewey took “Sound” and divided it into its component categories:

534.1 is the creation of sound
534.2 is the transmission of sound
534.3 is the characteristics of sound
534.4 is the measurement of sound

See, this is all super-logical! But PLEASE do not think that you must memorize each small number. That is what the database on your computer is for. The funny thing is just that the numbers WILL seep into you, and until then, when your computer points you to 534.2, you know that those books will be precisely about a particular facet of “Sound.” This is terrific for students doing reports on a particular topic, or simply curious about something! 

If 534.2 (the transmission of sound) needs to be broken down further, Mr. Dewey will do it for you. And he has. 

Maybe a better example would be in the zoology section (590s). You animal lovers will recognize the basis for Dewey’s subdivisions right away! Yes, instead of reinventing the wheel, he followed the animal classification system already in use. Believe it not, I’ve actually visited libraries that put ALL the animal books under that one number: 590. So, the books about birds and mice and jellyfish and sharks and deer and bugs and sponges and microscopic protozoans were all mixed! For a kid doing a report on a mollusk, that didn’t help much. This is just what Dewey was trying to avoid! So, he broke the 590s into ten main groups, following the classification system:

591 General zoology
592 Invertebrates
593 Protozoans
594 Mollusks
595 Other invertebrates
596 Vertebrates
597 Fishes and amphibians
598 Birds
599 Mammals

Oh, but what good is a subject like “other invertebrates” (595), really? That is why Mr. Dewey didn’t leave us stranded:

595.1 Worm-like animals
595.2 Arthropods
595.3 Crustaceans
595.4 Spiders (yuck!)
etc.
595.7 Insects (more yuck!)

So, does that first number to the right of the decimal make things harder? Or, easier?! I think the latter, because it means that I can walk right to the 595.4s (if I have a knife at my back) and find the books about spiders.

The same is true of the 599s, the section on mammals. I have also seen libraries that put all mammal books under just 599. If you consider how many books about VARIOUS mammals you already own, you can see that such is not very helpful, and too much time is wasted seeking the walrus books from amongst the platypus books. Again, Dewey to the rescue! He used the classification system we already had in our science classes!

599.1 Monotremes (the obscure spiny anteater and platypus)
599.2 Marsupials (those with pouches)
599.3 I won’t overwhelm you with the science words here, but we’ll talk about this section in a minute….
599.4 Bats (Chiroptera)
599.5 Whales, dolphins, etc. (Cetacea)
599.6 Another big science word
599.7 A broad group of hooved & carnivorous animals
599.8 Primates
etc.

Now, those are helpful numbers! But even that 599.3 section was awfully big, remember? So, Dewey divided it by ten again. Would you need to remember these additional numbers? Not really, but it is so great to have your books labeled thusly. The computer will point you to the right number, and there will be all the precisely grouped books on your shelves.

599.31 The toothless animals (armadillos, sloths, etc., known as Edentata)
599.322 Bunnies! C’mon, don’t they deserve their own number?
599.323 Rodents, ugh (I think Emily had the same comment)
599.33 The insect eaters, such as moles and shrews
etc.

Again, let the database (whatever one you use) do the hard work for you; don’t think of your brain as the ONLY repository for these numbers, just as you don’t rely on your brain to remember every phone number of every acquaintance and nor do you prohibit your friends from having longer phone numbers than you can remember, not when that phone number gets you connected. No, the phone book is your friend. In the same way, the computer will handle the detailed numbers; you will just use that data to print out your labels, and then you will shelve your books in this delicious order. And when someone asks you for books on minks, you don’t need to know which group of carnivores it is in (the Mustelidae), because you will instead type “Mink” into the search box of your database, it will show you a super-detailed number (since the “carnivore” group is so large), and you will smugly walk over to 599.74447 and hand Bobby a book about minks! It is that easy! You already knew you were headed to the 500s for science, to the 590s for Zoology, and to the 599s for Mammals, and then you let the computer guide your hand to the “mink” group. That’s all it takes! 

Oh, and Mr. Dewey made it possible for us to take those numbers we learned about special nations (like -73 for the USA) and apply it to other topics, when desired. So, if you really had a book just about the minks of the USA (and that seems to be pretty far-fetched), you’d have a number that was reeeeeally LONG, but it would tell you a ton. It would be 599.74447073. Now, that is about the most intimidating number I can imagine–on the surface–but each of these numbers are carrying “KNOWABLE” meaning. You already know the 599 (mammals), you already know the .7 for the carnivore group (and you know that the additional 4447 got you to the specific Mustelidae family of minks, but the computer did that remembering)…. Well, now you have your “0” as a divider (between subject numbers and regional numbers) and then you have your -73 for America. So, even if we blasted you with the hardest number imaginable (“Minks of the USA”)….it now has MEANING for you…! The intimidation is officially over!

Why do I suddenly want a mink coat, though?

Oh…I should mention that the numbers to the RIGHT of the decimal convey the sort of specificity that is appropriate to the topic. In the physics example we used first, it was the aspects of “sound.” In the zoology example, it was the TYPE of animal. But you can easily imagine that the subsets of the Art section would be drawing, oil-paint, mosaic, pottery, etc. That is logical. And in the history sections, those numbers to the right (as Emily pointed out) break down that nation’s history into sensical periods. So, the .3 won’t be the same detail in history or in art or in science, but it WILL be the logical next division of the particular topic. So, not to worry!!! We can relax and know that each sub-grouping makes sense!

This post is part of our Ask The Librarian series, a Card Catalog Project. You can find more like this here. And, we would love to connect with you! You can find us on Facebook here.