The use of the Paraclete in Against Praxeas Chapter 25 is simple normative New Testament, whether you agree with the Trinitarian view or not.
What follows Philip's question, and the Lord's whole treatment of it, to the end of John's Gospel, continues to furnish us with statements of the same kind, distinguishing the Father and the Son, with the properties of each. Then there is the Paraclete or Comforter, also, which He promises to pray for to the Father, and to send from heaven after He had ascended to the Father. He is called another Comforter, indeed; John 14:16 but in what way He is another we have already shown, He shall receive of mine, says Christ, John 16:14 just as Christ Himself received of the Father's. Thus the connection of the Father in the Son, and of the Son in the Paraclete, produces three coherent Persons, who are yet distinct One from Another. These Three are one essence, not one Person, as it is said, I and my Father are One, John 10:30 in respect of unity of substance not singularity of number.
Sometimes you talk of
polysemy, that a word can have more than one sense, yet all of a sudden here your mind goes blank.
Re polysemy in respect of Greek grammar of ἕν:
As I have pointed out before. Tertullian's argument is deeply flawed on account of Deut 6:4, which says God is
"one" <masculine>. Without taking Deut 6:4 into account, Tertullian's thesis is untenable.
Tertullian alludes to John 10:30 and to ἕν ("one" - Adj - Neuter Nominative Singular) ("I and the Father
are one <neuter>.") But <neuter> in the Greek doesn't have the necessary connotation of
<substance> that Tertullian puts on this
Greek gender. The grammatical connotations of ἕν are
polysemic. Other connotations are <spirit> and <origin> (i.e. approximating to a concept of divine ageny).
Per Winer (SECT. XXVII.] NUMBER AND GENDER OF NOUNS. p191) "The Neuter, Singular or Plural, is sometimes employed to denote a person, when the writer purposely expresses himself
in general terms, to avoid particularising the individual." So all that can be plausibly adduced is that Jesus and his Father are not "one person."
Agency Connotations of ἕν
As to <spirit>, Eph 4:4 also (i.e. in addition to Deut 6:4) accounts for why the terms "Spirit of Christ" and "Spirit of God" are used interchangeably:
E.g. Romans 8:9 (KJV)
But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
As to <origin>, John 8:42 "I proceeded forth and came from God; neither came I of myself, but he sent me."
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Ergo: the argument of Tertullian that Jesus <the man> and his Father are of one <essence/substance> in John 10:30 is not made out. For what is made out by one <essence/substance> is that they aren't distinguishable in any material aspect, even during Jesus's humanity. Yet if this is so, how could "
the Father [be] greater than [Jesus]” (John 14:28)? Of course, in (high) Trinitarianism, it can't be true - ever - even during Jesus's humanity; and which is another argument for why Tertullian's argument is wrong.
NB: Deut 6:4 presents a transcendent argument about God, which is that God is denoted and characterized by the Father.