Things have a "conventional existence" ("how they appear to the ordinary person," per Geshe Sonam Rinchen)
but there is a "true existence" which is "not phenomenal" (Hejinian, summarizing a Buddhist teaching) -- or, rather, that phenomenal things do not have a true existence?
Rinchen again: "all phenomena are dependent on other causes and conditions for their existence, so it is said that they are devoic of inherent existence or true existence or self-existence"
Hejinian again: "What we (humans) can perceive and cognize, then, is 'non-inherent existence,' which comprises all the things to which such terms as 'arising' and 'occurring,' as well as 'changing' and 'disintegrating' and so forth, can apply" (142)