Modal languages and bounded fragments of predicate logic (Q1267082)

The aim of the paper is to find natural fragments of first-order logic which have the ``nice'' properties of basic modal logic: decidability, the finite model property, interpolation, etc. First, the authors show that the finite-variable fragments are not suitable in this sense. Then they define the guarded fragment, in which only bounded quantification of the form \(\exists\overline y(R\overline x\overline y \& \phi(\overline x,\overline y))\) is allowed, and prove that it enjoys the nice properties mentioned above.