Prerequisite concepts
The value of a partial derivative depends on the value(s) of what is held constant
FIXME: Is this really a statement about paths? I don't think we have path-related concepts.
Representations used
Partial derivatives that do not have the same variable(s) held constant (at the same values?) are not the same derivative
There are experimental limits to how $small$ of a change can be measured
The derivative can be interpreted physically
The coefficients in a differentials equation are partial derivatives
FIXME