Necessary, because if it were not true — if financial reward is NOT the only incentive that can effectively motivate people to make new inventions — then we might not need patent rights in order to encourage new inventions.

Not necessary, because the author never compares the amount of proift made by an inventor and a manufacturer of the invention.

Not necessary, because even if the costs incurred by a typical inventor applying for patent rights are SIGNIFICANT in comparison to the financial benefit of holding patent rights, patent rights can still provide a financial incentive to invent. The costs might might be significant, but the benefits of a patent can still outweigh the costs to the inventor.

Not necessary, because the author’s argument doesn’t get into specific situations in which patent rights should or should not be granted. The argument is just that we should continue to grant patent rights, or else we won’t get new inventions.

The author’s argument doesn’t rely on any claims related to the relationship between the length of a patent right and the costs of inventing the product.