What is the difference between reliability-centered maintenance philosophy and condition-based maintenance philosophy.?

Reliability centered maintenance is way to determine most effective (technical and cost wise) approach.  It employs all maintenance techniques including real time monitoring, preventive , predictive , pro-active maintenance etc. 

Based on my understanding, condition monitoring is use of techniques that allow us to predict a failure before it happens. e.g. Vibration analysis system can detect a slightest frequency change in bearings and it gives enough time to plan and change the bearing before it fails. Thermal imaging is another technique that can help us predict a failure before it happens. Very useful in prediction of failures related to electrical equipment as well as selected mechanical equipment e.g. gear boxes.