There is a tradition that haiku is divided into two parts: real haiku, which are about nature, and senryu, which are about people. These basic divisions get redivided by whoever is doing the analysis. Elizabeth St. Jacques has three categories of haiku (the third one is an overlap of the first two), and in her article she has plenty of examples of how to tell one from another.
Michael Dylan Welch sees four categories, which he describes. He notes that the division between haiku and senryu is sharp and serious in Japan, but believes English-language poets and lovers of poetry can afford to do without the distinction.
Jane Reichhold gives us the sordid history of senryu and why the gulf between the two forms is so wide in Japan. She also tells us how one of the great early importers of haiku-form poetry was very selective in the ones he gave the English-speaking world. She goes further than Welch and makes a cogent argument for English poets to drop the very idea of senryu in favor of, simply, haiku. Her reasoning makes good sense to me, and I intend to follow it.
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In other haiku news, I learned yesterday that one of my haiku will be used at tinywords, the haiku site run by poet D. F. Tweney. So if you aren’t already, start reading tinywords daily for all the wonderful haiku found there and to, eventually, see this Catsignal classic.