Ideas generate increasing returns because they are nonrivalrous
Ideas are nonrivalrous, which means they can be used multiple times by multiple parties without fighting over some limited stock of them. Naturally, this means that when we double our other inputs, we do not need to also double ideas in order to generate at least double the output. If we do happen to increase our ideas as well, then we will get more than double the output and, therefore, increasing returns. Thus, the ability of ideas to generate increasing returns is linked to their nonrivalry.