While the relatively recent notion of 'deliberate' metaphors - metaphors that supposedly play a special role in communication - is contested among researchers, the debate lacks empirical grounding. This book presents the first large-scale study of forms and functions of deliberate metaphors in authentic spoken academic discourse. The author's comprehensive qualitative analyses of 23 US-American college lectures from four different disciplines demonstrate that deliberate metaphors occur in various forms and fulfill important communicative functions. While these findings may indicate the value of deliberate metaphors, the author's critical discussions of both identification and application of deliberate metaphors in authentic discourse also point out issues with the very concept of 'deliberate' metaphor.