The Question Mark Inside was commissioned by Dean and Chapter of St Paul's Cathedral as the first large-scale public artwork in the cathedral's history. It marked the 300th anniversary of the topping-out of Sir Christopher Wren's architectural masterpiece in 2008.
The project posed the simple question, 'What makes life meaningful and purposeful?' and invited responses from the public during the anniversary year.
In addition, a number of opinion formers was interviewed including novelist Howard Jacobson, philosopher A C Grayling and columnist Caitlin Moran.
The resulting stream of answers, from the domestic to the sexual to the sublime, was projected onto the exterior of the cathedral dome, the West Front at Ludgate Hill, and the interior of the Whispering Gallery from 8 to 15 November 2008.
The aim was to create a seemingly endless flow of possible meanings and purposes for life to illustrate the unanswerable nature of the question and the plurality of life projects committed to by different individuals.
Diversity was the only quality these different life projects had in common.
The Question Mark Inside implies that within this diversity there must be space for all: with or without faith, with or without disability, LGBT+ or straight, male, female or non-binary, young or old.
The Question Mark Inside also re-lit the cathedral to show Wren's architecture in a new light - literally - so that the familiar design would be 'seen' afresh during the week of tercentenary projections.
The text was presented against digital animations of blue spines of light which swept over the outside surface of the dome.
The same blue spines were replicated on the inside dome describing the curvature of the Eastern wall at the level of the Whispering Gallery.
On the West front, the spines moved within the confines of the central rising columns of the West Front portico underlining the striking rising verticals of Wren's design.
The Question Mark Inside is dedicated by Martin Firrell to the memory of film producer Simon Channing Williams.
The project opened as part of the Lord Mayor's celebrations and was seen by an estimated 1.5 million people.