Consciousness scientists have not reached consensus on two of the most central questions in their field: first, on whether consciousness overflows reportability; second, on the physical basis of consciousness. I review the scientific literature of the 19th century to provide evidence that disagreement on these questions has been a feature of the scientific study of consciousness for a long time. Based on this historical review, I hypothesize that a unifying explanation of disagreement on these questions, up to this day, is that scientific theories of consciousness are underdetermined by the evidence, namely, that they can be preserved "come what may" in front of (seemingly) disconfirming evidence. Consciousness scientists may have to find a way of solving the persistent underdetermination of theories of consciousness to make further progress.S cientists studying consciousness have been unable to settle two central de-bates in the field. The first is about whether subjects are conscious of more than they can report: some researchers believe that consciousness and reportability are equivalent (Dehaene & Changeux 2011; Naccache 2018), while others think that consciousness overflows reportability (Block 1995;Lamme 2010). The second debate is about the identification of the physical basis of consciousness (e.g., Boly, Massimini, Tsuchiya, Postle, Koch, & Tononi, 2017;Odegaard et. al. 2017). In this debate, theories according to which consciousness pervades the universe co-exist with theories suggesting that some specific parts of the cortex are responsible for consciousness (Dehaene, Charles, King, & Marti 2014;Tononi & Koch 2015). My goal is to understand why consciousness scientists do not reach consensus on these questions.1. Here and below, I rely on Simmons's interpretation ( 2001) of the differences between the Cartesian and Leibnizian views of the mind. Danziger has also provided a very similar interpretation of the opposition between the Cartesian and Leibnizian traditions (1980).[Cartesians] regard consciousness as wholly inseparable from mental activity. The same principle passed, through Locke, into the modern English school of metaphysics, and became a fixed idea with nearly all English writers on mental philosophy down to comparatively recent times. On the Continent, and especially in Germany, another and altogether different course was pursued. Leibniz denied the Cartesian dogma ab initia, and maintained the doctrine of unconscious perception, or latent thought, as a fact which can be verified throughout all the stages of animal life, and in the actual operations of the human mind.