Latin sis, contracted from si uis (‘if you wish’) and commonly attached to imperatives in early Latin, is usually translated as ‘please’, but some scholars have seen it as urgent rather than polite. Here, an examination of all the examples of sis in early Latin (chiefly Plautus and Terence) demonstrates that it is neither polite nor urgent and indeed has no function in the politeness system at all: its function is as a focus-marking clitic particle. This role was only one-step in the long process of development undergone by sis, from an ‘if you wish’ offering genuine alternatives to ‘please’ (at a time before the earliest surviving evidence), then by weakening to the focus-marking particle (in early Latin) and then to disappearance (in Classical Latin).