"Can I-" yes. yes you can.
What is Multiclassing? Multiclassing in 4th edition Dungeons & Dragons means taking a multiclass feat to gain some of the benefits of a second class. These benefits include more options for paragon paths and feats, and access to powers from the second class by spending additional feats. A character's primary and secondary classes are not equal; it's more like dabbling in a second class than splitting between the two.
Multiclassing is an important part of the Pathfinder game. It allows a greater degree of character customization than the Archetype rules alone, and allows the creation of characters with diverse skill sets. Pathfinder's multiclassing rules, allowing a character to simply choose which class to advance in at each level, are easy to apply and keep track of in the game. Unfortunately, these rules are not perfect, because they require characters to trade their highest-level class abilities for the lowest-level class abilities in the new class. While some classes, such as Fighter and Rogue, can handle this loss gracefully, spellcasting classes like Wizard and Cleric lose far more than they can possibly gain from this arrangement. Prestige Classes like the Eldritch Knight and the Mystic Theurge have been designed to compensate for this, but they impose an undue burden on characters designed for them both early in their careers, before they qualify for the Prestige Class, and later when they have reached the maximum level. Also, in order to allow the full range of multiclass combinations, there would need to be a separate Prestige Class for every possible combination of two (or more) base classes.
These are just a few examples of what it means to multiclass.
Because wizards run out of spells