This paper aims to uncover where the disagreement between illusionism and anti-illusionism about phenomenal consciousness lies fundamentally. While illusionists claim that phenomenal consciousness does not exist, many philosophers of mind regard illusionism as ridiculous, stating that the existence of phenomenal consciousness cannot be reasonably doubted. The question is, why does such a radical disagreement occur? To address this question, I list various characterisations of the term “phenomenal consciousness”: (1) the what-it-is-like locution, (2) inner ostension, (3) thought experiments such as philosophical (...) zombies, inverted qualia and Mary’s room, (4) scientific knowledge about secondary properties, (5) theoretical properties such as being ineffable and being intrinsic, and (6) appearance/reality collapse. Then I examine whether each characterization provides (i) a dubitable sense of phenomenal consciousness in which the existence of phenomenal consciousness can be reasonably doubted, (ii) an indubitable sense in which its existence cannot be reasonably doubted, or (iii) a gray sense in which it is controversial whether its existence can be reasonably doubted. By doing so, I show that there is no single sense of phenomenal consciousness in which illusionists and anti-illusionists disagree whether the existence of phenomenal consciousness can be reasonably doubted. I conclude that the disagreement between illusionists and anti-illusionists is fundamentally terminological: while illusionists adopt a dubitable sense of phenomenal consciousness, anti-illusionists adopt an indubitable sense of phenomenal consciousness. Because of the extreme vagueness and ambiguity of the term “phenomenal consciousness”, illusionists and anti-illusionists fail to see that they talk about different senses of phenomenal consciousness. (shrink)