Sourced

• You make 'em, I amuse 'em.
  • Statement about children, as quoted in Enter, Conversing (1962) by Clifton Fadiman, p. 108

• Nonsense wakes up the brain cells. And it helps develop a sense of humor, which is awfully important in this day and age. Humor has a tremendous place in this sordid world. It's more than just a matter of laughing. If you can see things out of whack, then you can see how things can be in whack.
  • As quoted in "Author Isn't Just a Cat in the Hat" by Miles Corwin in The Los Angeles Times (27 November 1983); also in Dr. Seuss: American Icon (2004) by Philip Nel, p. 38

• When at last we are sure
  You’ve been properly pilled,
  Then a few paper forms
  Must be properly filled
  So that you and your heirs
  May be properly billed.
  • You're Only Old Once! : A Book for Obsolete Children (1986)

• You can get help from teachers, but you are going to have to learn a lot by yourself, sitting alone in a room.
  • On becoming a writer, NY Times (May 21, 1986)

• Adults are just obsolete children and the hell with them.
  • On writing for adults, as quoted in Of Sneetches and Whos and the Good Dr. Seuss: Essays on the Writings and Life of Theodor Geisel (1997) by Thomas Fensch, p. 96

• I like nonsense, it wakes up the brain cells. Fantasy is a necessary ingredient in living. It's a way of looking at life through the wrong end of a telescope, which is what I do, and that enables you to laugh at life's realities.
  • As quoted in Wisdom for the Soul: Five Millennia of Prescriptions for Spiritual Healing (2006) by Larry Chang, p. 376

• Sometimes the questions are complicated and the answers are simple.
  • As quoted in Looking Tall by Standing Next to Short People, And Other Techniques for Managing a Law Firm (2007) by H. Edward Wesemann

• You know you're in love when you can't fall asleep because reality is finally better than your dreams.
  • As quoted in Somewhere in the Middle of Love (2007) by Lisa A. Lipscomb, p. 31

And to Think That I Saw It on Mulberry Street (1937)

• And that is a story that no one can beat,
  When I say that I saw it on Mulberry Street.

Horton Hatches the Egg (1940)

• I meant what I said,
  and I said what I meant
  An elephant's faithful,
  One hundred percent.

Horton Hears a Who! (1954)

• On the fifteenth of May, in the Jungle of Nool,
  In the heat of the day, in the cool of the pool,
  He was splashing... enjoying the jungle's great joys...
  When Horton the elephant heard a small noise.

• A person's a person, no matter how small.

• "My friends!", cried the elephant.
  "Tell me! Do tell!
  Are you safe? Are you sound?
  Are you whole? Are you well?"

• "You're going to be roped!
  And you're going to be caged!
  And, as for your dust speck -- hah!
  That we shall boil in a hot steaming kettle of Beezle-Nut Oil!"

• "Don't give up! I believe in you all.
  A person's a person, no matter how small!
  And you very small persons will not have to die
  If you make yourselves heard! So come on, now, and TRY!"

• "This", cried the Mayor, "is your town's darkest hour!
  The time for all Whos who have blood that is red
  To come to the aid of their country!", he said.
  "We've GOT to make noises in greater amounts!
  So, open your mouth, lad! For every voice counts!"

On Beyond Zebra! (1955)

• Oh the things you can find
  If you don't stay behind!

• In the places I go there are things that I see
  That I never could spell if I stopped with the Z.
  I'm telling you this 'cause you're one of my friends.
  My alphabet starts where your alphabet ends!

• So, on beyond Z!
  It's high time you were shown
  That you really don't know
  All there is to be known.

The Cat in the Hat (1957)

• The sun did not shine.
  It was too wet to play.
  So we sat in the house
  All that cold, cold, wet day.

• We looked! Then we saw him
  Step in on the mat!
  We looked! And we saw him!
  The Cat in the Hat!

How the Grinch Stole Christmas! (1957)

• "Maybe Christmas", he thought, "doesn't come from a store."
  "Maybe Christmas... perhaps... means a little bit more!"

• In Who-ville they say
  That the Grinch's small heart
  Grew three sizes that day!

Yertle the Turtle (1958)

• And today the great Yertle, that Marvelous he,
  Is King of the Mud. That is all he can see.
  And the turtles, of course... all the turtles are free
  As turtles and, maybe, all creatures should be.

One Fish Two Fish Red Fish Blue Fish (1960)

• From there to here,
  from here to there,
  funny things are everywhere.

• If you never did
  You should.
  These things are fun.
  and Fun is good.

Green Eggs and Ham (1960)

• Sam I am
  I am Sam
  I am Sam
  Sam I am.

• I would not like them here or there.
  I would not like them anywhere.
  I do not like green eggs and ham.
  I do not like them Sam I Am.

• Say!
  I like green eggs and ham!
  I do! I like them, Sam-I-am!

The Lorax (1971)

• "Mister!", he said with a sawdusty sneeze,
  "I am the Lorax, I speak for the trees.
  I speak for the trees, for the trees have no tongues,
  And I'm asking you, sir, at the top of my lungs" --
  He was very upset as he shouted and puffed --
  "What's that THING you've made out of my Truffula tuft?"

• I am the Lorax! I speak for the trees,
  Which you seem to be chopping as fast as you please;
  But I also speak for the brown Barbaloots,
  Who frolicked and played in their Barbaloot suits,
  Happily eating Truffula fruits.
  Now, since you've chopped the trees to the ground
  There's not enough Truffula fruit to go 'round!
  And my poor Barbaloots are all feeling the crummies
  Because they have gas, and no food, in their tummies.

• Unless someone like you cares a whole awful lot,
  nothing is going to get better. It's not.

• Catch! calls the Once-ler.
  He lets something fall.
  It's a Truffula Seed.
  It's the last one of all!
  You're in charge of the last of the Truffula Seeds.
  And Truffula Trees are what everyone needs.
  Plant a new Truffula. Treat it with care.
  Give it clean water. And feed it fresh air.
  Grow a forest. Protect it from axes that hack.
  Then the Lorax
  and all of his friends
  may come back.

• Now all that was left 'neath the bad-smelling sky
  was my big empty factory...
  the Lorax...
  and I.
  The Lorax said nothing
  just gave me a glance. Just gave me a very sad, sad backward glance.
  He lifted himself by the seat of his pants and i'll never forget the grim look on his face
  as he hoisted himself and took leave of this place through a hole in the smog without leaving a trace
  and all that the Lorax left here in this mess was a small pile of rocks with one word.
  UNLESS

Did I Ever Tell You How Lucky You Are? (1973)

• And suppose that you lived
  In that forest in France
  Where the average young person
  Just hasn't a chance
  To escape from the perilous
  Pants eating plants!

I Can Read With My Eyes Shut! (1978)

• The more that you read,
  The more things you will know.
  The more that you learn,
  The more places you’ll go.

• Young cat! If you keep
  Your eyes open enough,
  Oh, the stuff you will learn!
  The most wonderful stuff!

Oh, the Places You'll Go! (1990)

• You have brains in your head.
  You have feet in your shoes.
  You can steer yourself
  any direction you choose.
  You're on your own.
  And you know what you know.
  And YOU are the one who'll decide where to go.

• You won’t lag behind, because you’ll have the speed.
  You’ll pass the whole gang and you’ll soon take the lead.
  Wherever you fly, you’ll be the best of the best.
  Wherever you go, you will top all the rest.

• I'm sorry to say so
  But, sadly it's true
  That bang-ups and hang-ups
  Can happen to you.

• On and on you will hike, And I know you’ll hike far
  and face up to your problems whatever they are.

  You’ll get mixed up of course, as you already know.
  You’ll get mixed up with many strange birds as you go.

  So be sure when you step.
  Step with care and great tact
  And remember that Life’s a great balancing act.

  Just never forget to be dexterous and deft.
  And never mix up your right foot with your left.

• Will you succeed?
  Yes you will indeed!
  (98 and 3/4 percent guaranteed.)

Disputed

• Don't cry because it's over, smile because it happened.
  • Though sometimes attributed to Dr. Seuss without a citation of source, this is more often cited as merely an anonymous proverb.

Misattributed

• Those who mind don't matter, and those who matter don't mind.
  • Bernard Baruch in response to a question by Igor Cassini as to how he handled the seating arrangements at his dinner parties, as quoted in Shake Well Before Using: A New Collection of Impressions and Anecdotes Mostly Humorous (1948) by Bennett Cerf, p. 249; the full response was "I never bother about that. Those who matter don't mind, and those who mind don't matter." This anecdote is also quoted online at Chiasmus.com. It has also become part of a larger expression, which has been commonly attributed to Dr. Seuss, even in print, but without citation of a specific work: "Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind."