In “An Answer to the Question: What is Enlightenment?”, the eighteenth-century German philosopher Immanuel Kant responded to a big question buried in a little footnote. But you wouldn’t know it, because contemporary editions of Kant’s famous essay no longer reproduce the parenthetical directive that Kant’s original essay printed right under the essay’s title in the December issue of the Berlinische Monatsschrift in 1784: “S. Decemb. 1783. S. 516.” (See December 1783, p. 516). And, in fact, page 516 in the December volume of the Berlinische Monatsschrift 1783 has a footnote: “What is Enlightenment? This question is nearly as important as: what is truth? And should certainly be answered before one starts to enlighten! But I have yet to find it answered anywhere.”

Kant’s attempt to define enlightenment, then, was a reply to a specific question. The footnote to which Kant’s essay refers was published in an essay written by the Berlin pastor Johann Friedrich Zöllner, who had published several sermons in the Berlinische Monatsschrift. Zöllner’s essay, “Is it wise to no longer sanction marriage through religion?”, discussed whether it would be “enlightened” to no longer require clergy to officiate weddings.¹ Kant’s essay was addressed to a larger philosophical question, but also a particular question posed on a particular page in a particular periodical by a particular contemporary. And yet we tend to read Kant’s essay, and, thus, the Enlightenment, apart from these relationships and particular moments of printed address and response.

Footnotes like the one on the bottom of page 516 in Zöllner’s essay are visible traces of these mediated relationships, markers of conversations, references, connections, and the sociability of knowledge. They are also visible markers of legitimacy and authority. They demonstrate familiarity, identity, and knowledge. As Anthony Grafton writes with respect to the eighteenth-century origins of the footnote within the nascent discipline of history: “The footnote is bound up in modern life with the ideology and the technical practices of a profession.”² It is an element of the history of disciplinarity and scientific credibility.

The footnote is also one of several visual typographic practices that have shaped modern knowledge. Our effort to understand better the footnote’s place within the eighteenth century is part of a larger, on-going project that seeks to understand a range of visual practices of scientific notation in the past: whether it be footnotes that communicate authority and the relationality of sources; tables that bring together disparate forms of information into geometric relations; diagrams that provide abstract representations of intellectual procedures or natural phenomena; or illustrations that provide mimetic representations of objects in the world. In each of these cases, authors, editors, and publishers used a graphic process to convey information and make truth claims, often in a way that sought to reduce complexity. And contemporary scholars continue to use these processes in order to communicate well and more efficiently with one another. Instead of reproducing the entirety of another text, we cite it. Instead of reproducing all of the underlying data of a process, we transform it into a table of relations. Diagrams abstract more detailed processes into more formal essence. Even illustrations have an indexical relationship to the larger real-world phenomena they are meant to represent.

As we explain in greater detail elsewhere, our larger project is about bringing together the intersecting strands of research from the fields of book history, the history of science, and document image analysis to better understand the analytical unit called “the page image” and its role in the history of scientific knowledge. Our aim us to take seriously the page image in a double sense: first, as an image of a page, that is, to see the digitized page first and foremost as an image rather than a flawed mediation of text; and second to see the page itself as an image, as a visual unit rather than a primarily textual one. What have been the ways that the graphic practices of pages have underpinned the epistemic claims of scientific knowledge?

In this essay, we recount our process of using machine learning and classification algorithms to detect footnotes within the Eighteenth-Century Collections Online dataset (ECCO). ECCO represents one of the most complete digitized collections of a national publishing context within a specific historical period, consisting of over 100,000 volumes and 32 million pages published in Britain between 1700 and 1800. It has become a staple of research in the history of ideas, not just in Britain but for scholars of the Enlightenment more generally. We see the enrichment of collections like ECCO as a primary research goal for furthering historical understanding.

We discuss here the samples of training data that were collected and manually annotated, the different types of page-features that were used in the detection process, and the estimated accuracy of our predictions. The net result is metadata on the presence of footnotes within approximately thirty-two million pages of historical documents, which we share along with metadata regarding the initial training data used so that others can work with the same data. As we detail in Table 1, overall we are able to recall pages with footnotes with 67.87% accuracy and of those we achieve a precision of 96.2%. This suggests that there are a considerable number of footnotes we may be missing but that when we do detect them we do so with a very high degree of confidence. In addition to these summary statistics, we also provide users with an estimated percentage of footnoted pages per document, a table of all page IDs that have predicted footnotes on them, and finally the estimated probability of a footnote being present for all pages in ECCO. We see this as a first step in fully annotating ECCO according to our four visual categories of footnotes, tables, diagrams, and illustrations.

We want to emphasize from the outset just how challenging this process has been. “At first glance, all footnotes look very much alike,” writes Grafton, “[but] even a brief exercise in comparison reveals a staggering range of divergent practices.” As we quickly learned, discerning what constitutes a footnote in the eighteenth-century is by no means a straightforward process. Training machines to identify such visual ambiguity is even more difficult. One of the issues that will need further reflection are the trade-offs between the gains of acquiring knowledge at larger scale and the challenges introduced by a fundamental uncertainty surrounding historical evidence.

Overall, we see this project contributing to a larger effort of enriching digitized collections of historical documents with more information about the documents (what is traditionally called “metadata” or data about data). We see this particular effort as contributing to knowledge about the visual qualities of page images, with a specific attention to what we are calling the history of “scientific notation.” One of the major obstacles for historical understanding is the minimal amount of knowledge we have about individual documents within large document collections. We might think of this as a second-wave of digital history: the first—which is still on-going—involves the act of digitization itself. This effort is about making physical copies, which are geographically limited in their accessibility, more widely accessible to a broader reading public. The second wave, to which we see our work contributing, can be seen as the attempt to provide more knowledge about the composition of the collections to facilitate large-scale study of cultural history. ECCO metadata currently consists of features like publication date, author, title, publisher, and in some cases subject headings. There is much more that we can do to annotate collections. But to do so at large-scale requires developing algorithmic procedures for expertly labeling documents, which in turn necessitates greater collaboration between the humanities and the sciences.

However, it is important not to mistake these labels for what computer scientists call “ground truth.” All knowledge is situated. This project represents the coordinated efforts of a team of 14 researchers split between the humanities and computer science, including both students and faculty, ranging in levels from BA to Masters to Phd to Professor. It entailed a lengthy collaboration to create mutual understanding and shared goals as well as a clear understanding of the cultural object of study (in this case historical practices of footnotes). The training data assembled thus represents the understanding and prior knowledge of the humaities cohort, while the detection algorithms represent the understanding and prior knowledge of the computer science cohort. Any machine learning process inevitably encodes, explicitly and implicitly, these biases into its outputs and are thus not value free. While this may seem less controversial with a more straightforward visual object like footnotes, it is important that we continue to foreground the human learning behind machine learning. We now proceed to describe the process we used to annotate thirty-two million pages of ECCO.

[To read the entire article online, click here or here to read a PDF.]