Spinoza's use of the phrase “sui iuris” in the Tractatus Politicus gives rise to the following paradox. On the one hand, one is said to be sui iuris to the extent that one is rational; and to the extent that one is rational, one will steadfastly obey the laws of the state. However, Spinoza also states that to the extent that one adheres to the laws of the state, one is not sui iuris, but rather stands under the power [sub potestate] of the state (TP 3/5). It seems, then, that to the extent that one is sui iuris, one will not, in fact, be sui iuris. In this paper, I offer an interpretation of Spinoza's notion of being sui iuris that enables us to overcome this paradox and sheds light on Spinoza's relationship to the republican tradition. I work towards this goal by distinguishing between two ways in which Spinoza uses the locution, which correspond to two different conceptions of power: potentia and potestas. This distinction not only allows us to save Spinoza from internal inconsistency, it also enables us to see one important way in which Spinoza stands outside of the republican tradition, since he conceives of liberty not as constituted by independence, or citizenship in a res publica, but as being sui iuris in the first sense described above: being powerful.