For example, Joseph Priestley was a clergyman and educator, who spoke freely with others, especially those in his scientific community, including Benjamin Franklin, a self-made man who retired from the printing business. A system of patents was developed to allow inventors a period of time (often twenty years) to commercialise their inventions and recoup a profit, although in practice many found this difficult. The talents of an inventor are not those of a businessman, and there are many examples of inventors (e.g. Charles Goodyear) making rather little money from their work whilst others were able to market it.