Calvinism posits that in God there exists a distinction of wills; the will of revelation and the will of sovereignty (i.e. the revealed will and the secret or sovereign will). However, Arminians posit that the problem with this theory of two wills is that when one is put into effect then the other is put to naught. Let me make an example of this.
It is often said by Calvinists in Genesis 50:20 that God has commanded that it is unlawful to do ill to one’s family (in this instance, kidnapping). This is said to be the revealed will of God. And yet, allegedly in this Gen. 50:20 circumstance, Calvinists believe that you can also discern the operation of the sovereign or secret will of God working through the sin of Joseph’s brothers to a good and godly end.