Definition of "aphoristic"

Over and above all this, the method of the book is aphoristic; and, as might be expected from that method, without a plan; […]

1823, “Letters to a Young Man whose Education has been Neglected. Letter II.”, in Letters to a Young Man whose Education has been Neglected; and Other Papers (De Quincey’s Works; XIV), London: James Hogg & Sons, published 1860, page 35