Understanding Quantum Theory

There exist dozens of interpretations of quantum theory, but they do not seem to contribute much to understanding the theory. This paper attempts to clarify some issues that are discussed in those interpretations. The main keywords are: "Classical ontology", Indeterminism, Probability, Predictions, The necessity of classical concepts, Minimal interpretation, Lattice, Physical objects, Alternatives to quantum theory?, Measurement, Realism. One of the main points of this paper is the role of predictions in understanding any theory of physics.