My claim did not concern starting points in general. I’m not a relativist. But for mathematical formalisms, you have to accept the fact that many aspects depend on the convention you pick. For a good example, read my recent blog series here on BioLogos to see what stuff someone can do with Special Relativity by using a different convention.
It was my observation that the particular line of reasoning of 3 being special because 1+2=3 depends on a rather arbitrary assumption. If you restrict yourself to the collection of natural numbers, there is still an ambiguity of whether 0 should be included as being the first. See this Wikipedia entry for a discussion of natural numbers. Mathematical definitions of natural numbers vary in whether 0 or 1 is the first, because mathematicians agree that it essentially depends on one’s convention. If that doesn’t convince you, then we have to agree to disagree on that point.
So 1 apple + 1 banana + 1 pineapple = 1 fruit bowl. You see that the sum is different than the parts. But within categories it still works: 1 apple + 1 apple = 2 apples.
However, that doesn’t work with the Trinity.
The Father = God,
the Son = God,
the Spirit = God.
The Father + the Son + the Spirit = still one God, not three Gods.
Each person of the Trinity is fully God, yet they are God combined. 1 + 1 + 1 = 1
I believe the Trinity is a beautiful and logical teaching. But during the only course I ever had in divinity school, I was taught that there is no perfect analogy for the Trinity. So mathematics also fails to describe it. It reminded me of this small video clip on three heresies: modalism, arianism, and partialism.