Final answer:
The fifth argument of St Thomas Aquinas, concluding that all natural things are directed to their end by an intelligent being, is known as the Teleological argument. It is synonymous with the Design Argument and is different from the Cosmological and Ontological Arguments.
Step-by-step explanation:
The argument that an intelligent being exists by whom all natural things are directed to their end, as concluded by the fifth argument of St Thomas Aquinas, is called the Teleological argument. This is one of Aquinas’ Five Ways for demonstrating the existence of God, focusing on the presence of design in reality. Teleological arguments, or design arguments, are rooted in the observation of order, unity, complexity, and design in the universe, leading to the inference of an intelligent designer, commonly referred to as God. Aquinas's observation that things in nature are directed toward an end and require direction by an intelligent being, like an archer directing an arrow, forms the basis of his Teleological Argument.
In contrast, the Cosmological Argument is concerned with the existence and order of the entire cosmos, often calling upon the concept of an unmoved mover or a first cause, as presented by Aquinas in his other arguments. The Ontological Argument, on the other hand, is a philosophical meditation on being and existence, generally dealing with the concept and nature of God as a necessary being. The Design Argument is essentially synonymous with the Teleological Argument, drawing parallels between the complexity of the world and human-made objects, like a watch, to argue for the existence of a designer.