Situations serving as worlds as well as events in linguistic semantics are formulated as strings recording observations over discrete time. This formulation is applied to a linear temporal logic, in line with L. Schubert’s distinction between described and characterized situations. The distinction is developed topologically and computationally, and linked to the opposition between truth-conditional and proof-conditional semantics. For a finitary handle on quantification, strings are associated with situations not only on the basis of observation but also through derivation and constraint satisfaction. The constraints specified lead to an implementation simpler than the derivations given. © 2009 Elsevier Inc. All rights reserved.