how can an ablative absolute be recognised?

an ablative asolute is a neat little participle, which can be used to describe something which has happened in the past but is connected to what is happening in the main clause of the sentence, for example: 

with the camp having been captured, Caesar congratulated the soldiers

castris capitis, Caesar laudavit milites 

The alblataive absolute works as a prepersition to the main clause, it is recognisable by its ablative ending on the participle stem of the verb eg:

capio (present 1st person, group 3) 

capitus (participle past tense stem) 

capitis (ablitive plural participle - describing the ablitive noun it is attached with)    

the ablative absolute works like a noun and looks much like a noun, but it infact a participle!!!