Keyboard keys intermittently not working

On my Macbook Air (13-inch, early 2014), certain keys (space bar, delete, left arrow and apostrophe) are intermittently working. I have gone through the general troubleshooting (checking accessibility settings etc) and have resorted to using the keyboard viewer in place of the keys that don’t work. For the most part, none of the above keys are working, but sometimes all of them will work for a couple of minutes.