No, not circular reasoning at all. The gift of Faith enables me to believe without doubting whatever God has revealed. 
How do I find out what God has revealed?
Through the teaching of the Son of God, Our Lord, Jesus Christ passed down to us by His Apostles via the Traditio ad Apostolos and Holy Scripture.
Who determines this Tradition and Scripture? 
The Apostles who received it and their successors, the popes and bishops of the Church founded by Our Lord Himself to whom He gifted the charism of infallibily passing it on to future generations.
To be a Catholic is a desire to follow the teachings of Our Lord as bequeathed to us through His Church. 
Those who wish to decide for themselves what to believe and what not to believe are quite entitled to do so; what they are not entitled to do is pass on their own personal beliefs as Catholicism.