This paper is concerned with the extent to which individual members of governments reliably implement the decisions of the governments to which they belong, a matter which is rarely discussed, if ever, and yet can be critical for the operation of national executives. After a general presentation of the problem, the paper examines the reasons why members of collegial governments are more likely to be reliable than members of hierarchical governments. As ‘cabinet’ governments tend to be more collegial while ‘presidential’ governments tend to be more hierarchical, unreliability seems also more likely to take place in presidential governments, to the extent that these are indeed hierarchical. Progress in this area has been hampered so far by the absence of a tight operational definition of collegial and hierarchical governments: such a definition is presented here, opening the way for the empirical testing of the impact which the distinction may have on the reliability of members of governments.