There are physics concepts with circular definition. Like work and energy. For example: what is energy? Energy is capacity to do work. What is work? Work is energy being transfered to the system .... The same with charge, time. What else? Does existence of "circular" concepts implies that those concepts are 1) basic building blocks of universe; 2) we have little clue about them. However, we can use those concepts to describe world around us and make our lives easier. For example, in materials science, one can easily obtain a formula relating hardness of an alloy to its composition using design of experiment techniques. The formula will reliably predict hardness of the alloy. However, coefficients of that formula (and formula itself) are mostly meaningless. Does something similar occur in physics? "We have little clue what is energy. However, we can use that concept to our practical advantage". Is any hope to crack some circular concepts in the future?