"If two things are quite equal in all respects as much as can be ascertained by all means possible, quantitatively and qualitatively, it must follow that the one can in all cases and under all circumstances replace the other, and this substitution would not occasion the least recognizable difference."

I am not sure if I believe that any two things are exactly alike. I believe that there is always something, no matter how minor or small, sets two things apart. I don't believe that God would create anything the same; I believe He would make each individual or thing unique in his/her/its own way.