We all have that inner-voice, the one that runs a commentary on ourselves and actions. My own actually is the voice of my mother - who was a very big critic and bully in my life. Hence, my inner-voice is extremely critical. It reflects those messages I tended to receive during my formative years. I am guessing that you received the same.

This voice is not the same as the voices one hears when delusional or schizophrenic. I understand those are more 'separate' or disjointed.

In CBT I learned to call these critical ideas and 'phrases' from my inner voice are automatic negative thoughts. The therapy doesn't mean you no longer have these thoughts; rather, it gives you the skill to challenge them and consider there may be alternative positive thoughts instead. Interestingly, while the negative thoughts are in the tone of my mother's voice the positive thoughts (that more and more often champion over the negative) are in my own.