Can one solve these objections to substance dualism without invoking divine intervention?
2.Brain damage affects mind
3.Why do only living things with brains have consciousness?
So I understand the basic question to be:
is it possible to be a substance dualist without also being a theist?
The supporting questions then imply that the dualist must resort to a divine intervention to:
First off, I think the position can be rejected somewhat trivially in that there's no reason why a dualist must invoke divine intervention. I'm putting words in your mouth there (but for an important reason) Presumably you mean something more subtle along the lines of no explanation offered that does not invoke divine intervention is plausible or convincing. But then we must now ask plausible or convincing to whom?
Maybe to bypass all of that, we can look at some historical details. Historically, monism about matter (the idea there is only matter) was the view that was considered implausible for everyone -- including atheists, because:
These were real questions at the point when Locke was writing, and it took quite a bit of work for us to get to the point where these questions seem absurd.
It's not my particular specialization, but my sense is that there were dualist atheists because dualism does not require that the answer to your three questions must be "divine intervention". Moreover, theistic dualists don't even have to give that answer.
Descartes, being both a theist and a dualist, answers your first question with the pineal gland. That's not a "God did it answer" -- and to a good extent that is a deviation from the divine illumination theory used by Augustine and Aquinas to explain how we can think of things. If the standard is someone needs to find it plausible or convincing, then that standard is met.
With regard to your second question, there's an important problem that makes it a bit less important to answer, viz., the phenomenon of an apparently damaged mind doesn't prove damaged mind. This is actually an empirical problem of sorts -- a lot of the literature of mind/brain has shown that some things some things we've concluded from what someone can say or do in the world are not as indicative of their state as we imagined. (Cf. people who return from comas and the degree to which they said they were aware of their surroundings).
The third question is an interesting one, but a dualist merely has to believe there is mind that attaches to some bodies. Why wouldn't they just be living things? Why doe that require divine intervention?
tl;dr - no requirement to be a theist to be someone who believes in substance dualism, but that doesn't mean you would find any of their arguments convincing.
Welcome Noah. I don't think there's any logical connection between substance dualism and the existence of God.
Suppose we follow E.J. Lowe and define or characterise substance dualism as follows :
[Substance dualism] maintains that persons or selves - that is to say, self-conscious subjects of experience and agents of intentional actions - are distinct from their organic physical bodies and any parts of those bodies, such as their brains or central nervous systems. It regards persons as substances in their own right, in the sense of 'substance' in which this denotes a persisting entity and bearer of properties which does not depend for its identity on any thing other than itself. (E.J. Lowe, 'Non-Cartesian substance dualism and the problem of mental causation', Erkenntnis (1975-), Vol. 65, No. 1, Prospects for Dualism: Interdisciplinary Perspectives (2006), pp. 5-23 : 5.)
The nature of substance (supposing there to be such a thing) is that it is a persisting entity and bearer of properties which does not depend for its identity on any thing other than itself. The same would apply to the physical side of substance dualism if we regard (human) bodies as substances.
The nature of substance is not logically connected with any theory of the origin of substance or of the association of substances as in substance dualism. A substance might have any origin or none : there is absolutely no logical connection between X's being a substance - a persisting entity and bearer of properties which does not depend for its identity on any thing other than itself - and the existence of a God or any other agency that creates it.
Some have supposed that there is and ultimately can be only one bona fide substance, namely God. But that is a separate question. It is beside the point here anyway since substance dualism recognises substances other than God.
Someone who argues that it requires God to put the two substances together - to associate or align them - has gone beyond pure substance dualism by adding this extra element to the theory. Association or alignment could in any case come about, if in fact it does occur, in a variety of ways without God's intervention.
The answer by @virmaior is direct and probably complete, here I'll present some supplementary perspectives.
Considering your point 2, we can quickly find many instances where persons with severe disablement (brain damage, deaf, mute etc.) have found ways to communicate. Now if someone unable to communicate in the usual fashion can find alternative ways to express them self, presumably that means they applied some problem solving skills (thought). So if thinking and showing a desire to communicate, even beyond base necessity, then we would certainly ascribe consciousness to such a person. We won't suspect their mind is damaged, rather we would say they have physical limitations. This brings us to your third point:
Since material limitations can prevent us from detecting the full measure of mind of an object/person/animal, we are completely unable to detect whether starfish "have consciousness". I'm not saying rocks can think, I'm saying nobody asked them. And if anyone asked, they couldn't hear them. And if they don't have ears to hear, why would they ever speak? Bottom line is that if we admit Substance Dualism, we admit there are things beyond the usual physical means of detection, I.e. only a mind could detect them.
I'm trying to explore point 1 in these questions:
"divine intervention" cannot be objectively proven. (at least not yet)
There are alternative possibilities for causal interaction.
Yes, we don't need to say God did it, but we cannot say how.