Quilibet vult esse beatus quia appetere beatitudinem nihil aliud est quam appetere ut voluntas satietur.
Everyone desires to be happy because to desire happiness is nothing else than to desire that one's will be satisfied, and this everyone desires.
Ratio autem beatitudinis communis est ut sit bonum perfectum, sicut dictum est. Cum autem bonum sit obiectum voluntatis, perfectum bonum est alicuius, quod totaliter eius voluntati satisfacit.
For the general formal aspect of happiness consists in its being the perfect good, as has been said above. But since good is the object of the will, the perfect good of a man is that which entirely satisfies his will.