text: Monotonic reasoning is a byproduct of the fact that OWL and SWRL are based on logic. The OWL 
  reasoners are essentially theorem provers. If you have ever studied mathematical proofs, you know that 
  one of the classic ways to prove that something is invalid is to show that some variable has two different 
  values. E.g., if our theorem implies that p = True and p = False then we have a contradiction. Each 
  variable can only have one value. This is why SWRL rules can only add values to variables rather than 
  change them. For more on this see the excellent presentation on SWRL by Martin O’Connor: 
  https://protege.stanford.edu/conference/2009/slides/SWRL2009ProtegeConference.pdf 
  
  This is why SPARQL often needs to be used rather than SWRL even though SWRL is more abstract and 
  powerful. SWRL does not support non-monotonic reasoning whereas SPARQL does. Similarly, when 
  validating data, we may want to take actions to change it, e.g., to coerce it into a proper standard format. 
  To do that we need to change rather than add a value, i.e., we need non-monotonic reasoning. 