 One of the earliest qualitative probability logics is Hamblin’s (1959). The language is extended with a unary operator \(\Box\), which is to be read as ‘probably’. Hence a formula such as \(\Box\phi\) is to be read as ‘probably \(\phi\)’. This notion of ‘probable’ can be formalized as sufficiently high (numerical) probability (i.e. \(P(\phi)\geq t\), for some threshold value \(1/2 &lt; t \leq 1\)), or alternatively in terms of plausibility, which is a non-metrical generalization of probability. Burgess (1969) further develops these systems, focusing on the ‘high numerical probability’-interpretation. Both Hamblin and Burgess introduce additional operators into their systems (expressing, for example, metaphysical necessity and/or knowledge), and study the interaction between the ‘probably’-operator and these other modal operators. However, the ‘probably’-operator already displays some interesting features on its own (independent from any other operators). If it is interpreted as ‘sufficiently high probability’, then it fails to satisfy the principle \((\Box\phi\wedge\Box\psi) \to \Box(\phi\wedge\psi)\). This means that it is not a normal modal operator, and cannot be given a Kripke (relational) semantics. Herzig and Longin (2003) and Arló Costa (2005) provide weaker systems of neighborhood semantics for such ‘probably’-operators, while Yalcin (2010) discusses their behavior from a more linguistically oriented perspective.