In the period 1945-1980, it was generally believed that patent law did not pertain to software. However, it now appears that some people have received patents for algorithms of practical importance–e.g., Lempel-Ziv compression and RSA public key encryption–and are now legally preventing other programmers from using these algorithms.

This is a serious change from the previous policy under which the computer revolution became possible, and I fear this change will be harmful for society. It certainly would have had a profoundly negative effect on my own work: For example, I developed software called TeX that is now used to produce more than 90% of all books and journals in mathematics and physics and to produce hundreds of thousands of technical reports in all scientific disciplines. If software patents had been commonplace in 1980, I would not have been able to create such a system, nor would I probably have ever thought of doing it, nor can I imagine anyone else doing so.