Theophrastus took over the leadership of the Peripatetic school after Aristotle. This work seems to have been an introduction to a larger work, or set of works, in the genre of physics/metaphysics. It mostly consists of him ruminating on questions regarding first principles.
It is interesting that Theophrastus was not above questioning some of his master's views. He finds problems in both Plato's and Aristotle's systems when it comes to motion/movement (kinesis). With Aristotle he sees it as inconsistent that a first mover could set into motion bodies with disparate forms of motion, e.g. planets move differently. With Plato he finds it problematic that the forms could be both at rest and in motion apart from sensible reality.
Quite an interesting little work. I do intend to read some more of Theophrastus in the not too distant future. Many of his works are fragmentary, but he was an important figure in the tradition of Aristotelianism. ( )