The Cambridge History of English and American Literature in 18 Volumes (1907–21).
Volume IV. Prose and Poetry: Sir Thomas North to Michael Drayton.
§ 2. Origin of the Quartos
On the other hand companies refrained from publication. They sought by this means to increase the profit from their performances. Thus, Thomas Heywood speaks of some of his plays being “still retained in the hands of some actors, who think it against their peculiar profit to have them come in print.” But this shortsighted policy on the part of the companies did not prevent others from supplying the demand for printed copies which naturally existed. In the absence of any strict laws of copyright, it is not surprising that publishers were found ready to snatch a profit by the surreptitious publication of the more popular plays of so favourite a writer as Shakespeare.