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The conceivability objection

That we can imagine a world does not entail that it is possible: our concepts are not the measure of the real.

Objects to Property dualism

Loar · "Phenomenal States" · 1990

1. The argument moves from "I conceive a double without experience" to "such a double is possible", then to "experience is not physical". Everything turns on the first move.
2. Yet one could conceive, without contradiction, water that was not H₂O: it was nonetheless impossible, water being H₂O wherever there is water. What we conceive depends on what we know, not on what is.
3. If experience is a cerebral state, conceiving a brain without experience amounts to conceiving a thing without itself: the description's apparent coherence comes from our having two distinct concepts of it, grasping that state in two ways, from outside by measurement and from inside by living it, without yet knowing it is the same.
4. The argument therefore assumes, without showing it, that whatever is imagined without contradiction can exist: its conclusion is already lodged in its premise.

Therefore The zombie proves nothing until that step is justified: the gap may lie only in our concepts, between two ways of grasping one and the same state.