 All of these assumptions are controversial. Some philosophers have explored the view that the fundamental parthood relation is three-place (Thomson 1983; Hudson 2001; Balashov 2008; Donnelly 2010; McDaniel 2014; Lafrance 2015) or four-place (Gilmore 2009; Kleinschmidt 2011). Others have argued that one fundamental parthood relation holds between regions, another between material objects (McDaniel 2004, 2009). And some have argued that there are no fundamental parthood relations (or other fundamental mereological relations, such as overlapping). Of these philosophers, some propose reductive definitions of parthood, whereas others eliminate parthood (Dorr 2005; Sider 2013; Cowling 2014a), though the distinction between reduction and elimination is sometimes blurry.