Final answer:
The figure of speech used is an oxymoron, combining contradictory terms to highlight the complex nature of love.
Step-by-step explanation:
The figure of speech used in the line 'love is heavy and light' from Shakespeare's works is oxymoron. An oxymoron is a figure of speech that combines contradictory terms to create a unique and contrasting effect. In this case, Shakespeare juxtaposes the contrasting qualities of 'heavy' and 'light' to emphasize the complex and paradoxical nature of love. This oxymoron highlights how love can be both burdensome and uplifting at the same time.