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We build a general equilibrium model where growth is driven by two invention types: fundamental ideas that cause creative destruction, and derivative ideas that enhance the value of existing inventions. The model provides a new mapping from microeconomic, patent data to aggregate total factor productivity growth and the aggregate value of privately owned knowledge. We show how to measure the frequency of derivative ideas and the rate of creative destruction. We estimate that derivative ideas account for 70–80% of all patents and their presence more than doubles the value of knowledge capital relative to what the measured innovation rate might otherwise imply.