Social obligation begins far before people establish explicit cooperative relationships. Research on trust suggests that people feel obligated to trust other people even at zero acquaintance, thus trusting complete strangers even though they privately expect to be exploited. Such obligations promote mutually beneficial behavior among strangers and likely help people build goodwill needed for more long-lasting relationships.

Gottlob Frege is considered a founder of analytic philosophy and mathematical logic, but the traditions that claim Frege as a forebear never embraced his Begriffsschrift, or “conceptual notation”—the invention he considered his most important accomplishment. Frege believed that his notation rendered logic visually observable. Rejecting the linearity of written language, he claimed Begriffsschrift exhibited a structure endogenous to logic itself. But Frege struggled to convince others to use his notation, as his frustrated pedagogical efforts at the University of Jena illustrate. Teaching Begriffsschrift meant using words to explain it; rather than replacing spoken language, notation became its obverse in a bifurcated style of argument that separated deduction from commentary. Both registers of this discourse, however, remained within Frege's monologue, imposing a consequential passivity on his students. In keeping with Frege's visual understanding of notation, they learned by silently observing it, though never in isolation: notation and language were always mixed together.

The Pueblo population of Chaco Canyon during the Bonito Phase (AD 800–1130) employed agricultural strategies and water-management systems to enhance food cultivation in this unpredictable environment. Scepticism concerning the timing and effectiveness of this system, however, remains common. Using optically stimulated luminescence dating of sediments and LiDAR imaging, the authors located Bonito Phase canal features at the far west end of the canyon. Additional ED-XRF and strontium isotope (87Sr/86Sr) analyses confirm the diversion of waters from multiple sources during Chaco’s occupation. The extent of this water-management system raises new questions about social organisation and the role of ritual in facilitating responses to environmental unpredictability.

Doris suggests thought-provoking directions for rehabilitating moral agency within a self that is unaware and incoherent. These directions suggest more radical proposals. First, moral reasoning may serve many different functions beyond merely expressing a person's values. Second, social collaboration may not focus on moral reasoning as much as it does on the “defeaters” of that agency. Ultimately, moral agency may not reside in the individual but in social communities or within external situations.

In glacial environments particle-size analysis of moraines provides insights into clast origin, transport history, depositional mechanism and processes of reworking. Traditional methods for grain-size classification are labour-intensive, physically intrusive and are limited to patch-scale (1 m2) observation. We develop emerging, high-resolution ground- and unmanned aerial vehicle-based ‘Structure-from-Motion’ (UAV-SfM) photogrammetry to recover grain-size information across a moraine surface in the Heritage Range, Antarctica. SfM data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning, and were found to be accurate to within 1.7 and 50 mm for patch- and site-scale modelling, respectively. Grain-size distributions were obtained through digital grain classification, or ‘photo-sieving’, of patch-scale SfM orthoimagery. Photo-sieved distributions were accurate to <2 mm compared to control distributions derived from dry-sieving. A relationship between patch-scale median grain size and the standard deviation of local surface elevations was applied to a site-scale UAV-SfM model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0.3 km2 area of moraine. This highly automated workflow for site-scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis.

Climatic fluctuation is often cited as a major factor in the collapse of Maya civilisation during the Terminal Classic Period (e.g. Luzzadder-Beach et al.2016). Evidence of how people dealt or failed to deal with it has only recently become a more widespread focus for archaeologists. Investigations at Xcoch in the Puuc Hills show the various ways in which resident populations sought to manage water stores when faced with a climate prone to drought and other meteorological extremes. The study also presents results from the analysis of nearby speleothem laminae, which indicate that severe episodes of flooding and droughts may have contributed to a collapse in the population around AD 850.