Ro 9:18 Therefore hath he mercy on whom he will have mercy, and whom he will he hardeneth. 1. Hardening has its only internal source with the fallen human nature. 2. Hardening is a process and is progressive rather than a punctilliar event - Rom. 1:18-32. In Romans 1:18-32 suppression of the truth and digression in to hardening is the only option mentioned as this is necessary response of the fallen nature due to what it is. 3. Every member of the fallen race when the facultiy of conscience and intellect are sufficiently mature to comprehend and recognize light as light always respond initially by resistance and rejection due to what fallen nature "IS" - Rom. 8:7-8; Jn. 3:19-20. 4. Every cognant fallen member of the human race is in the process of hardening. 5. The process or progression is mapped out for us in Romans 1:21-32 and Psalms 1:1 and all fallen cognant mankind is somewhere in this process. 6. Spiritual ability or the ability to see, hear and respond to light is only and inseparably inherent in the new heart given by God - Deut. 29:4; Ezek. 36:26-27; 2 Cor. 4:6; etc. 7. The climax of hardening is found described in Romans 1:32 and Psalm 1:1c. God can save fallen man even in the final stage as Paul was so hardened to the light that he expressed himself in its uttermost form - destroying God through killing those expressing that light through them. He can also freely choose to not save them but glorify himself in their just damnation. CONCLUSION; The fallen nature is the source and cause while hardening is the necessary consequence and is contempoary with the fallen nature. The extent of hardening is due to exposure to light and the kind of response (searing, choosing to directly confront and/or deal with the light they are exposed to).