From 1971 until his death in Bali, Indonesia, he was a fellow at the Research School of Social Sciences (RSSS) at the Australian National University in Canberra.
In 1972, Sylvan (in a paper co-authored with Plumwood) proposed semantics for certain relevant logics that had been developed by American philosophers Nuel Belnap and Alan Ross Anderson.
[8] Not long after meeting Priest, and then investigating a logic capable of handling such true contradictions, Sylvan also endorsed the view.
From early in his career (and for many years after), Sylvan defended a sophisticated Meinong-inspired ontology (which he called "noneism"), first presented in his 1966 paper, "Some Things Do Not Exist.
[13] The view—also defended in recent years by Priest[14]—utilizes a modal theory including "impossible worlds" to deal with supposed objects, like the "round square."
[21] From his work in environmental ethics, Sylvan took an interest in anarchism, contributing an often-cited entry on the subject to A Companion to Contemporary Political Philosophy.