[Note: Mistaking a definite ὁ θεός as the subject would have been very likely, since the object of one clause often becomes the subject of the following clause—for example, vv. 4–5 switch from life > light > darkness in succession. Furthermore, since both θεός and λόγος are established, the omission of the definite article serves to portray θεός as though it were new information. The choice to emphasize θεός virtually precludes the possibility of including a definite article with this noun. To do so would introduce all kinds of problems from a discourse point of view as to the identification of the topic.]
See the preceding post for the explanation of P2.
Yet another reason the Arian/Jehovah's Witness reading of John 1 is wrong...to beat a dead horse—again.