> If you've taken Calculus, you've already worked with math that requires the infinitesimal to exist. Not at all. Standard calculus uses standard real numbers,

> If you've taken Calculus, you've already worked with math that requires the infinitesimal to exist. Not at all. Standard calculus uses standard real numbers, for which there is no infinitesimal. One may well speak of infinitesimals as a mental tool when building a mental model for calculus, but those infinitesimals are not actual real numbers (or a well-defined mathematical object at all - in standard calculus).