A mobile ad hoc network is a self organized cooperative network that works without any permanent infrastructure. This infrastructure less design makes it complex compared to other wireless networks. Lot of attacks and misbehavior obstruct the growth and implementation. The majority of attacks and misbehavior can be handled by existing protocols. But these protocols reduce the total strength of nodes in a network because they isolate nodes from network participation having lesser reputation value. To cope with this problem we have presented the Possibility and Certainty model. This model uses reputation value to determine the possibilities and certainties in network participation. The proposed model classifies nodes into three classes such as certain or HIGH grade possible or MED grade and not possible or LOW grade. Choosing HIGH grade nodes in network activities improves the Packet Delivery Ratio which enhances the throughput of the MANET. On the other hand when node strength is poor we choose MED grade nodes for network activities. Thus the proposed model allows communication in the worst scenario with the possibility of success. It protects a network from misbehavior by isolating LOW grade nodes from routing paths.