This article defends the existence of _borderline consciousness._ In borderline consciousness, conscious experience is neither determinately present nor determinately absent, but rather somewhere between. The argument in brief is this. In considering what types of systems are conscious, we face a quadrilemma. Either nothing is conscious, or everything is conscious, or there’s a sharp boundary across the apparent continuum between conscious systems and nonconscious ones, or consciousness is a vague property admitting indeterminate cases. Assuming mainstream naturalism about consciousness, we ought (...) to reject the first three options, which forces us to the fourth, indeterminacy. Standard objections to the existence of borderline consciousness turn on the inconceivability of borderline cases. However, borderline cases are only inconceivable by an inappropriately demanding standard of conceivability. I conclude with some plausible cases and applications. (shrink)