[2] Carl Jaenisch, who was an early advocate of the French and Sicilian defences, rejected this use of the term "irregular", saying that openings should rather be classified as "correct", "incorrect" or "hazardous".
[3] In The Chess-Player's Handbook (1847), for many years the standard English-language reference book on the game of chess, Howard Staunton accepted Lewis's overall classification system while tacitly acknowledging Jaenisch's objections.
Without assenting to the propriety of this distinction, I have thought it advisable, for the sake of perspicuity, to adopt a general and well known classification in preference to arranging these peculiar débuts under separate and less familiar heads."
An element that many irregular openings share in common to their favor, however, is that many players have not studied the resulting positions in depth.
This advantage can offset the theoretical weakness; even if the other player avoids any direct blunders, they may be forced to spend time deriving the correct move through personal analysis, rather than instantly knowing the "correct" reply from a memorized opening book.
In the same way, such strategies could be effective against older and weaker computer chess programs from the 1980s and 1990s: a chess program that heavily relied on memorized opening books from games of top players could be set adrift quickly by an irregular opening, and forced to calculate moves for itself.