John Davidson was widely recognized as the founding father of fluidization in chemical engineering. He was a great thinker and had a tremendous ability to distill complicated problems into much simpler concepts. Much of his thinking was set out, along with that of his coauthor David Harrison, in their book Fluidised Particles, first published in 1963, a book that is still used today. John was still coming into his office in Cambridge until the very last weeks of his life, where he continued to work with final-year undergraduates and graduate students. Fluidization, and two-phase flows, continued to fascinate him, and that enthusiasm was transmitted to those around him. The following article was the last work that he wrote and was very much a reflection on his life and career. John passed away on Christmas Day 2019, with the article in its final stages of preparation.

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