story identification - Man can do magic by writing spells on the inside of his mind

I'm trying to identify a fantasy fiction (possibly epic fantasy) book I read several years ago, although I'm sure it was out well before then. It may or may not be in a series, but it was a decently thick hardcover book I found in the adult section of my local library. The book was set in medieval times (there were castles and a lord's solar), and the main character is able to perform magic by closing his eyes and concentrating on emptying his mind, kind of like a blackboard, and then mentally writing out the spells or symbols. I think he learns to do this during the book.

I seem to recall part of the plot being an effort to try to free somebody (a woman, perhaps) from an enemy's castle, but I'm not completely sure about that. I do remember the characters ride horses and fight with swords and there were also archers at some point: It's not just magic. I realize this is pretty vague.

Answer

Sounds like one of Gordon Dickson's Dragon series. In the second book of the series, The Dragon Knight, protagonist Jim is taught use of his magical power by the wizard Carolinus. This turns out to involve clearing his mind, treating the inside of his head as a blackboard, and 'writing' spells on it in a simple symbolic pseudocode-like language.

For example, Jim's most commonly used spell ("turn into a dragon") is

NOTSHAPE ME -> DRAGON

The language isn't a true object-oriented magic language (though it made me want one); it's a channel for his thoughts. He often creates new and silly object nouns on the fly, as when looking out for magical traps from the bottom of an enemy's tower:

ME/SEE -> MAGIC WORKSABOVEINRED

(The effects are consistent with the spell cast, however. Later Jim is caught out by a magical trap beneath him - specifying 'above' was a mistake.)

The solar you mentioned is in Jim's castle, which he takes from an evil knight in the first book, The Dragon and the George. The woman he rescues would probably be his wife Angie, whom he rescues from evil wizards in a dark tower at the end of that book. (He is not yet a wizard at this time, though he is a dragon for most of the first book - that being the premise.)

Nearer the end of the series Dickson dumped this system and let Jim move on to the because-I-say-so magic used throughout by his mentor.