Discrete event dynamic systems may have extremely large state spaces. For their analysis, it is usual to relax the description by removing the integrality constraints. Applying this idea, continuous P/T systems are defined by allowing fractional firings of transitions, and thus the existence of non-discrete markings [4, 5, 1]. In this paper we compare the behaviors of discrete and continuous systems, and observe that they are not necessarily similar. The problems that appear lead to the definition of two extensions of reachability. Many properties shall be extended differently depending on which reachability definition is being considered. Here, we concentrate on liveness and deadlock-freeness, proposing extensions and relating them to their discrete counterparts.