What is the correct answer and why?

Article |, Section 8 of the United States Constitution grants Congress the power: "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries..." Part of the way Congress has acted on this power is by passing laws allowing inventors to obtain patents. What is a "patent"? What is the point of granting the property right known as a \"patent\" to an inventor