The rhetorical device of parataxis is the juxtaposition of clauses and sentences but without employing connecting words:

I'm tired and going to bed; you stay here.

or

I was late in getting to class; professor gave me a dirty look.

In both examples, normal English syntax (the way words are ordered or placed in a sentence and connected to form a sentence) would dictate that the writer use a coordinating or subordinating conjunction--"I'm tired and going to bed, but you stay here" or "I was late in getting to class, and the professor gave me a dirty look."  The technique is often used to create an appearance of abruptness.  Probably the most famous example of parataxis is Caesar's "Veni; Vidi; Vici," which means "I came;I saw;I conquered," which has an abrupt but powerful effect because each action is as important as the next one.

In Frank O'Hara's poems, we see many examples of parataxis.  For example, in "Why I Am Not a Painter," we find

I am not a painter, I am a poet. . . . Well, for instance, Mike Goldberg is starting a painting. I drop in. 'Sit down and have a drink,' he says. I drink; we drink.

By avoiding the use of conjunctions (and, but, for, or, etc.), O'Hara achieves abrupt but concrete imagery that would be softened by the use of conjunctions between independent clauses.  Literary critics have often described parataxis as masculine and assertive because there are no links between declarative sentences like "I am not a painter, I am a poet."

In O'Hara's poem "Ave Maria," parataxis achieves both an abruptness and a stream of consciousness that moves the reader forward very quickly:

. . . . and when you grow old as grow old you must/they won't hate you/ they won't criticize you/ they won't know/ they'll be in some glamorous country/ they first saw on a Saturday afternoon. . . .

O'Hara is giving the mothers of America advice to let their children go to the movies, and the effect of parataxis is that we move quickly through O'Hara's argument as if we are viewing images every second on a movie screen.

O'Hara again uses parataxis very effectively in his poem "Having a Coke with You":

. . . .partly because in your orange shirt you look like a better happier St. Sebastian/partly because of my love for you, partly because of your love for yoghurt/partly because of the fluorescent orange tulips around the birches. . . .

As you can see, the lack of linking words (conjunctions and subordination) establishes the equality of all these qualities and, more important, we rush through these images because there are no natural hesitation points that would be signaled by linking words.

Parataxis is quite common in the works of skilled writers, but O'Hara adopted the technique as a hallmark of his poetry in order to create concrete imagery quickly and to make the images equal.  In other words, every image created by parataxis is equal in importance and effect--much like images flashing on a movie screen with no narrative to connect them.