In this paper the author attempts to make clear how Thomas Aquinas interpreted on the famous expression of Aristotle's Metaphysics: all men by nature desire to know. According to Aquinas, the proposition has three meanings. The third is that a human being seeks to connect with separate substances, which will bring a perfection to human intellect and the ultimate happiness to men.
Although this studious appetite is natural, there are few who can finally reach to know them. Aquinas says the reason is as follows. It is difficult for a human being to find out the truth about insensible immaterial things. If there are any obstacles, we would not be able to know about them. But in this case the disturbance lies in the knowing precisely.
The desire to know the truth, not the knowing precisely, can be either straight or crooked. When a person seeks to know the truth about creatures without heeding a righteous end, namely knowing about God, the inordinateness of the studious appetite to discover will cause vice. Moderation as a virtue is necessary in this case.
The necessity of the knowledge derived from a revelation of God must be considered here, but not only to remove obstacles to know. Because the hankering to connect with separate substances can be crooked as a desire to know the truth, it is necessary for human reasoning to have the recognition of God as a rightful end. This is a characteristic interpretation of Aquinas about a natural desire for knowing, both in his Summa theologiae and in his commentary on Aristotle's Metaphysics.