Can you believe in one and believe in the other too? I believe so. They actually both work together for the glory of God. One is God’s calling and empowerment, and the other is our choice and will-power. The Bible says:
“And we know that all things work together for good to them that love God, to them who are the called according to his purpose. For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren. Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified” (Romans 8:29-30).
Again, Jesus says to His disciples, “Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you” (John 15:16). Unto those who He receives into heavenly dwelling, Jesus also pronounces: “Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world…” (Matt 25:34).
It is a mystery of His grace and justice, that some are called and empowered and shown great mercy…while some have only a frightening expectation. Jesus said concerning His disciples that no one can come to Him, unless the Father draws them (John 6:44). God, who knows all things, knew before hand those who would truly receive Him and love Him and do His will… Regardless, our free-will was not forsaken the day we were chosen…