Gordon Clark on the Trinity

"One substance or essence means that neither the Father nor the Son is an 'essence.' Each is a 'person.' Only the Trinity as such is an 'essence.' The confusion here and in the footnote above disappears, or at least is alleviated, by using the word definition instead of essence; and also by remembering that the Son has an 'essence' that is different from the 'essence' of the Father, but which in both cases contains the 'essence' of Deity. The definition of Deity does not define the Son; nor can the definition of the Son apply to Deity. A succulent does not have all the qualities of a cactus, but the latter has all of the characteristics of the former. That is to say, the Trinity or Godhead, absolutely and as such, does not have the characteristics of any one Person, absolutely and as such; but each Person has all the predicates of Deity. Note that the word here is Deity, not Father." - Gordon Clark, The Trinity