A theoretical novelty, or TN, is the first move in a known opening position that has never been played in recorded practice, typically the product of home preparation.
Opening theory is the sum of everything already played and published. A theoretical novelty is the move that steps off that map: in a position with an established body of games, someone plays a move no one has tried before. Chess Informant marked such moves with an N, and the shorthand TN stuck.
Great novelties are prepared, not improvised. The most famous is Frank Marshall's 8...d5 against Capablanca in New York 1918, a gambit reportedly saved up for years, which launched the Marshall Attack that remains core Ruy Lopez theory a century later. In the engine era novelties are usually computer-checked at home and often appear deep in known lines, sometimes past move twenty.
A novelty is not automatically good: it is merely new, and plenty of novelties are refuted the same evening. Its practical power is asymmetric knowledge, since the novelty's author knows the analysis while the opponent must solve everything at the board. Club players rarely need genuine novelties; the lesson is the value of preparing concrete ideas in your own openings.
No, only a new one. Annotators mark the first departure from known theory whether it is brilliant or a blunder. The novelties that matter are the prepared ones backed by analysis, which force the opponent to find precise replies alone at the board.
Yes, constantly, they just happen deeper in the theory tree. Engines both create and consume them: teams search for playable moves engines undervalue at first glance, and a strong novelty today might be an idea on move eighteen of a well-known line.
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