Javadocs sounds like a cut and paste error. The pluggable belief system is a new feature in development, to extend the traditional TMS system. The first implementation for this now implements a full JTMS system, instead of the more simple approach Jess, Clips and Drools. JTMS allows for logical insertions to have positive and negative labels. A logical insertion cannot exist n the network, while there is a negative version of it. https://github.com/droolsjbpm/drools/blob/master/drools-compiler/src/test... I mentioned this back last november. http://lists.jboss.org/pipermail/rules-dev/2012-November/004283.html "Just added a Justification based Truth Maintenance System to Drools, so now you can do contradictions. http://www.cis.temple.edu/~giorgio/cis587/readings/tms.html https://github.com/droolsjbpm/drools/blob/master/drools-compiler/src/test... https://github.com/droolsjbpm/drools/blob/master/drools-compiler/src/test... https://github.com/droolsjbpm/drools/blob/master/drools-compiler/src/test... It works just like normal logical inserts, but now there is an optional second argument. That argument can be "neg" or "pos", the default is "pos" if the argument is omitted. If you have both positive and negatives then no fact is available to the WM - because it's in conflict. If you have all positives then the fact is propagated as normal, if you have all negatives then the fact is propagated in the "neg" partition" Davide also has a defeasible logic implementation written that plugs into this belief system, but I still need to merge in his code, for people to try it. Once all of this is ready, it'll be available in a beta release and information placed in the new & noteworthy. Mark On 19 Feb 2013, at 12:55, Wolfgang Laun <wolfgang.laun(a)gmail.com&gt; wrote: