William Shedd's Systematic Theology this year as part of my devotional reading. I had heard of Shedd but never read him. I found him in my Logos Bible Software when I was looking something up lat last year and really enjoyed what I was reading. On the doctrine and nature of God, he leans toward philosophy but is a stretch for me but also something I wanted to read, especially when considering the trinity. Here Shedd talks about the nature of the personality of God. He mentions modes but is not referring to modalism which he will note later his discussion the trinity.
In discussing the subject of the personality of God, we have seen that this involves three distinctions in the infinite essence. God cannot be self-contemplating, self-cognitive, and self-communing, unless he is trinal in his constitution. The subject must know itself as an object and also perceive that it does. This implies, not three distinct substances, but three distinct modes of one substance. Consequently, divine unity must be a kind of unity that is compatible with a kind of plurality. The unity of the infinite being is triunity or Trinity. God is a plural unit. Shedd, W. G. T. (2003). Dogmatic theology. (A. W. Gomes, Ed.) (3rd ed., p. 220). Phillipsburg, NJ: P & R Pub.