Since 2014, substantially gainful has been defined by regulation as being the maximum annual amount a person could earn on CPP Disability. For 2016 that amount was $15,490 per year. So basically they are saying you have the capacity to earn $15,000 or more per year working part-time. This is theoretically possible, but would be a challenge for most people unless you have higher level education and ability to earn a high hourly rate working part time. I think you should keep appealing this because this is just a standard thing they say to lots of people. Fill out the free consultation form on our website and our people can communicate you via email.