Adventitially

1691, Arthur Gorges (translator), The Wisdom of the Ancients by Francis Bacon (1609), London, Preface, But if any do obstinately contend, That Allegories are always adventitially, and as it were by constraint, never naturally, and properly included in Fables, we will not be much troublesome, but suffer them to enjoy that gravity of Judgment, which I am sure they affect, although indeed it be but lumpish, and almost leaden.