Explain the economic case for governments encouraging private investment in knowledge and technology

Knowledge behaves partly like a public good: once created it can be copied cheaply, and one firm's use does not stop another's. A firm investing in research captures only part of the return, because spillovers benefit rivals, suppliers and customers. The social return exceeds the private return, so firms reject projects whose private return falls below their cost of capital even when the social return clears it, and the economy underinvests in research. That gap justifies R&D subsidies and tax credits, funding for basic research, patents and education spending. In endogenous growth models such policies can raise long-run growth. The trap is justifying support by private profitability rather than by spillovers.