We hear a lot at times about the godhead, so that got me wondering: what is the Scriptural basis for the Christian doctrine of Modalism?
I don't think that the distinction between Modalistic, Economic, and Hypostatic Trinitarianism is reducible so simply to differing Scriptural bases. Scripture simply does not bother to be so explicit and precise on the matter of the inter-relation between the Three as we do.
Rather, the debate is grounded firmly in the more abstracted realm of philosophical theology. That is, from the same texts all three positions argue differing conclusions. The "Scriptural basis" for one would be identical, typically, I believe, to the "Scriptural basis" for another (if we were to compensate for the natural variety that individuals bring to the conversation inherently). The debate really sparks upon the effects that these conclusions have upon various other doctrines. One's model of the Trinity tends to have rather noticeable ripple-effects upon the framework of one's entire theology (systematically speaking), and it is on this basis, I believe, that the debate finds its primary academic motivation (though, no doubt, there are other, say, psychological motivations for the debate, as well).