 Thus, consider the following three propositions: (i) The triangle has three angles, (ii) The substance exists, and (iii) The triangle exists. Proposition (i) is clearly self-explanatory, since the essence of the triangle (which contains the nature of the number three and the nature of an angle) is the sufficient reason for its having three angles (adding any other information is of no explanatory value). Spinoza considers proposition (ii) as self-explanatory as well. Notice that Spinoza does not define substance (in E1d3) as existing by virtue of its essence, but rather derives this claim from the definition of substance (in E1p7). In contrast to (i) and (ii), the existence of a triangle does not follow merely from its essence (since it is caused by entities external to the triangle, and therefore has to be explained through these external causes).