Underlie/ˌʌndərˈlaɪ/ Definition 1 of 3Pro Tip 1/3Cause and Effect Use 'underlie' to connect a basic cause with its complex effect. The desire for freedom underlies many historical revolutions. Pro Tip 2/3Abstract Foundations 'Underlie' often refers to abstract foundations, like principles or concepts. Ethical considerations underlie the new policy. Pro Tip 3/3Implicit Presence What 'underlies' is not always immediately visible but is present throughout. Careful planning underlies the event's success.