Let me clarify. The vast majority of protestant denominations profess Trinitarianism and reject Modalism. However, that doesn't mean that the average Protestant on the street neccessarily understands what the doctrine of the Trinity is about.
I'm not too sure about that. I would agree that the vast majority of Protestants who are educated on the Trinity are not modalists, but there are lots of Protestants "on the street" who will describe God in modalistic (not to mention Arianistic) terms.
Sorry for being a Johnny-come-lately to this thread, but just had to mention that not all Protestants adhere to a flawed view of the Trinity. My family is Southern Baptist, and since my conversion, many of the elder members of my family have investigated our theology and emphatically agree with Orthodox Trinitarian doctrine, including rejection of the Filioque (or rather the implications thereof. Being Baptist, they reject creeds outright). This agreement in Trinitarian theology is a major reason why they have quit proselytizing, and in fact, outright approved of my conversion.You are correct. In fact, the vast majority of Protestants are not Modalists.
Anyway, my point is that there ARE in fact some Protestants who hold correct Trinitarian beliefs. Our friend Cleopas seems, based on my reading of the thread, to be included in that number.
I apologize if my post seemed to accuse Protestantism at large of holding Modalist beliefs. Quite the contrary, I was simply clarifying that there are some reformed Protestants do hold the same Trinitarian beliefs as the Orthodox Church, i.e. rejecting the implications of the Filioque clause. This was meant to be in response to deusveritasest's sweeping generalization that all Protestants affirm the Filioque (or for non-credals, the implications thereof), thus resulting in their worship of a different God.
I must admit, based solely on my past experience in various Reformed traditions (before conversion was a lifelong Baptist, and attended many Bible studies in Presbyterian, Trinitarian Pentecostal, and Nazarene churches), I would venture to say that you are correct in noting that your average (I'll narrow it down to Reformed) Protestant does not really grasp the doctrine of the Trinity. I can't speak for Magisterial traditions, as I really have no experience with those, aside from attending two or three Christmas Eve services in a Methodist church as a child. I will say that in all my years as a Baptist, it was NEVER preached on. The summation of our exposure to the Trinity was being baptized in the name of the Father, Son, and Holy Spirit, as well as one traditional hymn ("Holy, Holy, Holy") that I remember saying "God in Three Persons, Blessed Trinity", but that song got phased out with the rise of contemporary Protestant worship music (read: pop-rock with shallow lyrics). However, there really are some relatively "informed" Protestants who actually know the in's and out's of their tradition's confessions.