Run-on Sentence

In grammar, sentence and clause structure, commonly known as sentence composition, is the classification of sentences based on the number and kind of clauses in their syntactic structure. Such division is an element of traditional grammar.

Run-on sentences
A run-on sentence consists of two or more independent clauses (i.e., clauses that have not been made dependent through the use of a relative pronoun or a subordinating conjunction) that are joined without appropriate punctuation: the clauses "run on"--into confusion rather than clarity, like intersecting streets without signs for Yield or Stop. The independent clauses can be "fused", as in "It is nearly half past five we cannot reach town before dark", in which case the two independent clauses might be separated (between "five" and "we") with a period [...five. We...], a comma and conjunction (...five, and we...), or a semicolon (...five; we...). The independent clauses can be joined inadequately with only a comma (the comma splice). James Joyce's novel Ulysses employs stream of consciousness, which takes literary license by intentionally breaking this grammatical rule by use of long, punctuation-free, run-on sentences, particularly in the final chapter "Penelope".

In general, run-on sentences occur when two or more independent clauses are joined without using a coordinating conjunction (i.e. for, and, nor, but, or, yet, so) or correct punctuation (i.e. semicolon, dash, or period). A run-on sentence can be as short as four words, for instance: I drive she walks, or even I drive, she walks, because in these short cases there are two subjects paired with two intransitive verbs. An imperative sentence like "Run walk" can be a run-on even if it only has two words.

While some sources view comma splices as a form of run-on sentence, others limit the term to independent clauses that are joined without punctuation.

Per The American Heritage Dictionary of the English Language, the term "run-on sentence" is also used for "a very long sentence, especially one lacking order or coherence".