"Darkness is to space what silence is to sound, i.e., the interval"

This quote by Marshall McLuhan is drawing a comparison in between darkness and silence. In the same way that silence is an interval or a pause in noise, darkness is an absence of light or a pause in space. It suggests that darkness is not just the reverse of light, but rather an essential part in producing space and enabling light to be perceived. Likewise, silence is not simply the absence of sound, but a period that enables sound to be viewed more clearly.