I first heard the words "absence of evidence is not evidence of absence" as a first-year archaeology undergraduate. I now know it was part of Carl Sagan's retort against evidence from ignorance, but at the time the non-ascribed quote was part of the intellectual toolkit offered by my professor to help us make sense of the process of excavation.
Philosophically this is a challenging concept, but at an archaeological site all became clear in the painstaking tasks of digging, brushing and trowelling. The concept was useful to remind us, as we scrutinised what was there, to take note of the possibility of what was not there. What we were finding, observing, and lifting, were the material remains, the artifacts which had survived, usually as a result of their material or the good fortune of their deposition. There were barely recordable traces of what was there — the charcoal layer of a prehistoric hearth for example — and others recovered in the washing, or the lab, but this was still tangible evidence. What the concept brought home to us was the invisible traces, the material which had gone from our reference point in time, but which still had a bearing in the context.
It was powerful stuff which stirred my imagination. I looked for more examples outside philosophy. I learned about the great near-Eastern archaeologist, Sir Leonard Woolley who, when excavating the 3rd millennium BC Mesopotamian palace at Ur, modern day Iraq. There, he conjured up musical instruments from their absence. The evidence was the holes left in the excavation layers, the ghosts of wooden objects which had long since disappeared into time. He used this absence to advantage by making casts of the holes and realising the instruments as reproductions. It struck me at the time that he was creating works of art. The absent lyres were installations which he rendered as interventions, and transformed into artifacts. More recently the British artist Rachel Whiteread has made her name through an understanding of the absent form, from the cast of a house to the undersides and spaces of domestic interiors.
Recognising the evidence of absence is not about forcing a shape on the intangible, but acknowledging a potency in the not-thereness. Taking the absence concept to be a positive idea, I suggest interesting things happen. For years middle-eastern archaeologists puzzled over the numerous, isolated bath-houses and other structures in the deserts of North Africa. Where was the evidence of habitation? The clue was in the absence: the buildings were used by nomads who left only camel prints in the sand. Their habitations were ephemeral, tents which, if not taken away with them, were of such material that they would too disappear into the sand. Observed again in this light, the ariel photos of desert ruins are hauntingly repopulated.
The absent evidence of ourselves is all around us, beyond the range of digital traces.
When my parents died and I inherited their house, the task of clearing their rooms was both emotional, and archaeological. The last mantelpiece in the sitting room had accreted over 35 years of married life, a midden of photos, ephemera, beach-combing trove and containers of odd buttons and old coins. I wondered what a stranger — maybe a forensic scientist, or traditional archaeologist — would make of this array if the narrative was woven simply from the tangible evidence. But as I took the assemblage apart in a charged moment, I felt there was a whole lot of no-thing which was coming away with it. Something invisible, and unquantifiable, which had been holding these objects in that context.
I recognised the feeling, and cast my memory back to my first archaeological excavation. It was of a long-limbed hound, one of those 'fine, hunting dogs' the classical writer, Strabo, described as being traded from ancient Britain into the Roman world. As I knelt in the 2000 year old grave, carefully removing each tiny bone, as if engaged with a sculptural process, I felt the presence of something absent. I could not quantify it, but it was that unseen 'evidence' which, it seemed, had given the dog its dog-ness.