Valid “If….then” logical statements can be combined. Take these two:
Calicos are cats. If something is a cat, then it has a tail.
We get Ca* –> C and C –> T. They can be combined using the common variable:
Ca –> C –> T. We can also simply conclude Ca –> T (Calicos have tails)**. This becomes extremely important.
Make Sure Things Match
“Fish live only in water. Fish have gills.” You can’t combine those to form a longer chain.
F –> W and F –> G
You can only combine from necessary to sufficient, not sufficient to sufficient.