Relationship between state & religion in Tomas Aquinas's thought

Governors’ scope of authority in sacred &secular affaires, and also extent of influence &effect of religion & clergymen in political affairs, has been regarded as one the significant issues through history of political practice and thought, which has led to separation or proximity and mixture of religion and politics in both theory & practice. This article seeks through studying Thomas Aquina's thoughts, as the greatest philosopher and theologian of catholic Christianity and one of the greatest claimant of composing philosophy and religion, the answer of how did he find the relationship between religious and political affairs, and how & how much his opinions is used in modern thoughts, Therefore, afterstudying the bases of his thought, which were effective in his political opinions, the relationship between religion and state in regard to his Christy-Aristotelian principles and then these relations in regard to his theories on law is assessed.