The literary critic Peter Craven calls the essay an 'odd mongrel thing'. And he's right. Sometimes it looks like the best journalism; sometimes its style more closely resembles fiction. It can shapeshift from the stilted version required of school students to a flowing meditation on consciousness and a solar eclipse in the manner of Annie Dillard. Its flexibility allows it to be used by writers to comment on their childhoods, their travels, their hobbies and their politics. In this respect, it's curiously democratic. Anyone can use it to express themselves - and on issues that matter - without claiming expertise in any particular field.