 Given this account of Descartes’s epistemology, we can now see that both cognitio and scientia are varieties of, not only knowledge, but certainty as well. This is an important point to note, for it means that certainty cannot be straightforwardly characterized in terms of indubitability. For a belief known with certainty to be immune to doubt—not merely at a moment but absolutely—it must be embedded in a coherent system of beliefs, all of which are known with certainty (for a similar account of Descartes’s epistemology, see Sosa 1997, though Sosa takes cognitio to be a lower grade of knowledge than scientia; also, see Loeb 1992 on the importance of stability for Descartes’s epistemology). Scientia, or systematic certainty, represents an admirable, but probably unattainable, goal. If humans are capable of certainty at all, it is surely of the sort that is capable of mixing with doubts.