Her starting point is this argument:
1. There is only one God.
2. The Father is God.
3. The Son is God.
4. Therefore, the Father is the Son. (p. 1)
She (I think, justifiably) brushes aside “relative identity” escapes from this argument. (I won’t open this can of worms here; the curious can see here.) She argues that a theologically adequate theory of the Trinity must meet four conditions:
(i) secure the distinctness of the Persons, (ii) maintain monotheism, (iii) affirm that each… Person of the Trinity is God and (iv) affirm that the Trinity of Persons is God. Arguably Sabellianism as I shall understand it meets all these conditions and [in contrast to relative identity theories] does not require any ad hoc philosophical commitments. (p. 2)
Next time: What is this wonderful “Sabellianism”?