Wizardry was first practiced around year -40,000. It caries on the tradition of "word magic" a form of magic as old as the world itself. Word magic uses the spoken word to shape magic into a useful form. Thus wizard spells must always be spoken, with the rare exception of great wizards who need only to formulate the words of the spell in thought.
Wizardry was popularized in the age of Warring Wizards (-7,000 to -4,000) and most of the spells used today were devised at that time. Because many of those wizards were "renaissance" men of magic (practicing many forms of magic) wizardry is now known as one of the most universal, basic, and adaptable forms of magic. It is said that wizardry is the closest to the true shapeless form of magic. The evidence for this is its incalculatably large collection of spells, and also the variety of uses the spells can be put to.
The original language of wizardry is often refurred to as "Sage Elvish" a form of ancient elvish that was used by the first group of elvish wizards. However, most of its newer spells were created at the time of warring wizards in a more modern elvish tongue. Most spells are a combination of words from varying eras in elvish language. Why certain combinations work and others do not is a mystery to wizards.
Historicly it makes sense that a wizards magic is derived from words. In western culture there is a huge emphasis on the power of words. The word of god. God allowing man to name the animals. Basically in naming the animals man has dominion over them. Notice how the name of God is not to be spoken. His attributes are not to be discribed. Its all about once you can name/ discribe something you have a power over it.