raw_thought wrote:If my experience of a visualized triangle is private, it is by definition a quale.
A quale is defined as an intrinsically private experience.
A materialist believes that there are no private experiences.
For him there is no subjective reality. For him only objective reality exists. Therefore, for him it is impossible to visualize a triangle because my visualized triangle is dramatically subjective, it is private.
You are misunderstanding what a materialist is.
Materialism provides a methodology by which we can understand the "objective" world, but all materialists know that this is a task that has to be performed carefully as they fully realise that senses can be deceiving, and opinion has to be overcome with evidence.
You are committing a deep conceptual error. There really is no such thing as a materialist in the way you want to caricature him. The best materialists are those that know that they have to overcome their subjective world in order to understand the physical world more perfectly. And it is the Empiricists, and Idealists working within a Materialist framework over the last 200 years or more that have utterly transformed our understanding of the world.
I sometimes walk on the pavement. When I do this I can be considered a pedestrian, and I have a set of rules, and rights as a pedestrian over the drivers of vehicle. I also own and use a car. When I am driving my BMW I am no longer a pedestrian but a road user and have a set of rules that guide and govern my behaviour.
Right at this moment I am a blogger. But that does not mean I am not a road user, nor a pedestrian.
There is no phrase which can exhaustively describe something; least of all a person. There is no "materialist" that is not also something else too.
The idea of the qualia is a useful one, but your example is a poor one. Triangles are analytic devices that can be conveyed and understood by others objectively. Colour is not. Colour is a better example.
Qualia do not disprove the worth of materialism. They highlight that human experience is not directly in accord with the objective material world, which, by implication, we can never know precisely though we are comprised of it.