Sleep is divided into two different states which alternate through the night: Dream Sleep sometimes referred to as REM (rapid eye movement) and Deep Sleep.
As we pass from one state to the other, we often wake, roll over and go back to sleep, totally unaware that we have woken at all. This is because we have sleep clues – dark room, comfy bed, etc. A baby needs to ‘learn’ his sleep clues. If these sleep clues are being breastfed, rocked to sleep or a dummy, he will need these clues again when he wakes at night.
You can teach him new clues which will enable him to fall asleep on his own.