PS: There's still a nuance that might require clarification(or am I adding confusion?) in your original quote though: Quote: "(of course, free software license

PS: There's still a nuance that might require clarification(or am I adding confusion?) in your original quote though: Quote: "(of course, free software licenses would still fulfil the important function of contractually requiring the publication of modified source code)" Even though as many others have pointed out, OSS licenses can be contracts, I'm actually not sure this sentence is correct. When somebody uses the source code in compliance with the license terms, a contract might be formed to allow both parties to enjoy rights. However, if one party never complied with those terms and breaches them (eg. distributing source without retaining copyright notices), then arguably no contract was ever formed, and the act is a simple matter of copyright violation and not a "breach of contract". Hope I'm not splitting hairs. Disclaimer: learned English common law a bit, not a lawyer.