A spell sage has mastered spells of all types, and is able to increase the effectiveness of his own spells and eventually even cast spells from other classes' spell lists. While most wizards focus on a school, the spell sage looks at the particular aspects of individual spells and is not afraid to modify them with interesting bits of insight to gain a deeper understanding of the formulae.
At 1st level, once per day the spell sage's understanding of spells allows him to increase his caster level by 4 for a single spell he casts. He can do this twice per day at 8th level and three times per day at 16th level. This ability replaces arcane bond.
At 2nd level, the sage's understanding of the spells of bards, clerics, and druids is so great that he can use his own magic in an inefficient, roundabout way to duplicate those classes' spells. Once per day, a spell sage can spontaneously cast any spell on the bard, cleric, or druid spell list as if it were a wizard spell he knew and had prepared. The casting time for this spell is 1 full round per spell level of the desired spell (using the lowest spell level if the spell is on more than one of the spell lists indicated above) and requires expending two prepared spells of that spell level or higher; if the spell's casting time is normally 1 full round or longer, this time is added to the spell sage's casting time. For example, if a spell sage wants to use spell study to cast cure light wounds (cleric spell level 1st), he must spend 2 full rounds casting and expend two prepared wizard spells of 1st level or higher.
At 6th level and every 5 levels thereafter, a spell sage can use this ability an additional time per day (to a maximum of four times per day at 16th level). This ability replaces arcane school.