The authors develop a theory of ground logics which are nonmonotonic formalisms in the spirit of the McDermott--Doyle nonmonotonic modal logics. The ground logics are intended to formalise reasoning of rational agents who are allowed to make nonmonotonic assumptions only on information concerning the real world and expressed by nonmodal formulas. Reasoning in the ground logics is \(\Pi_3^p\)-hard, i.e., it is, in general, computationally harder than reasoning in the nonmonotonic modal logics. On the other hand, the ground logics have several epistemically interesting properties, e.g., they naturally capture justification-free defaults. Apart from the computational complexity of reasoning, semantical questions are addressed as well. The ground logics are characterized in terms of a Shoham-style preference semantics [see also \textit{D. Nardi} and \textit{R. Rosati}, Lect. Notes Comput. Sci. 990, 225-236 (1995)].