In this paper we give a financial justification, based on non arbitrage conditions,of the (H) hypothesis in default time modelling. We also show how the (H) hypothesis isaffected by an equivalent change of probability measure.[...]

We consider backward stochastic dierential equations (BSDEs) witha particular quadratic generator and study the behaviour of their solu-tions when the probability measure is changed, the ltration is shrunk,or the underlying probability space is transformed.[...]