Using the made-up language Babel-17, Samuel R. Delany looks at how language shapes how we think and how we live our lives. In this respect, many of the novel's most important quotes relate to the structure of language.

The novel starts with a quote by the Italian American linguist Mario Pei:

Nowhere is civilization so perfectly mirrored as in speech. If our knowledge of speech, or the speech itself, is not yet perfect, neither is civilization.

From there, Delaney looks at the strangeness of language within the framework of a galaxy made up of many alien worlds. For example, at one point the main character Rydra gives an account of the language of the Ciribians, who have technological know-how beyond any human understanding, but don't have a word for house. What they can do, she says, is

describe it to another Ciribian who never saw it before so that the second can build an exact duplicate, even to the color the walls are painted . . . where each circuit is located, how big it is, in short completely describe the whole business in nine words. Nine very small words, too.

Rydra is hired by the government to decipher what they think is the code of Babel-17. As Rydra states emphatically, however, Babel-17 is not a code, but a language.

There are two types of codes. Ciphers, and true codes. . . . A code can be one type or the other, or a combination. But both have this in common: Once you find the key, you just plug it in and out comes logical sentences. A language, however, has its own internal logic, its own grammar, its own way of putting thoughts together . . . There is no key you can plug in to unlock the exact meaning.

Rydra extends this theme when she has to explain the concept of the word "I" to Butcher.

"Do they have this word, I?"

"As a matter of fact they have three forms of it: I-below-a-temperature-of-six-degrees-centigrade, I-between-six-and-ninety-three-degrees-centigrade, and I-above-ninety-three."

The Butcher looked confused.

"It has to do with their reproductive process," Rydra explained. "When the temperature is below six degrees they're sterile. They can only conceive when the temperature is between six and ninety-three, but to actually give birth, they have to be above ninety-three."

Finally, here is a quote that sums up Delany's theory of language:

Well, most textbooks say language is a mechanism for expressing thought. But language is thought. Thought is information given form. The form is language.