Defying polarization, U.S. support for marijuana legalization grew from 36% to 67% during 2005-2019 (Pew Research Center, 2019). To identify discourse properties that accompanied this shift, we present the largest social media corpus on the topic (>3M documents) and the first to target Reddit (2008-2019). We used geolocation inference to distinguish U.S. discourse from international chatter and separate pre- and post-legalization content given marijuana’s uneven legal status across U.S. states. Research on online discourse has focused on generalized statements (e.g., moral arguments/sentiments). However, we combine topic modeling with hierarchical clustering to show that personal anecdotes and attitudes were a major driver of discourse especially during the legalization drive, at the expense of certain more generalizable themes. We classified comments by expressed attitude and presence of persuasion attempts using neural networks to show that the anecdotal discourse reflected not only social sharing, but also active argumentation.

Narratives (sequences of purposively related concrete situations) and arguments (reasoning and conclusions in an attempt to persuade) are distinct cornerstones of human discourse. While theories of their linguistic structures exist, it is unclear which theorized features influence perception of narrative and argument quality. Furthermore, differences in their usage over time and across formal versus informal mediums remain unexplored. Thus, we use an original dataset of news and Reddit discourse (consisted of >10,000 clauses), annotated for clause-level discourse elements (e.g., generic statements vs. events; Smith, 2003), and their coherence relations (e.g., cause/effect; Wolf & Gibson, 2005). We identify the features that correspond to differing perceptions of narrative and argument quality across multiple dimensions. Since the documents cover marijuana legalization discourse during a period of massive attitude shift in the U.S. (2008-2019), we also examine changes over time in discourse structure within this rapidly evolving sociopolitical context.

Text-generation algorithms like GPT-2 (Radford et al., 2019) and GPT-3 (Brown et al., 2020) produce documents which resemble coherent human writing. But no study has compared the discourse linguistics features of the artificial text with that of comparable human content. We used a sample of Reddit and news discourse as prompts to generate artificial text using fine-tuned GPT-2 (Grover; Zellers et al., 2019). Blind annotators identified clause-level discourse features (e.g., states and events; Smith, 2003), and coherence relations (e.g., contrast; Wolf and Gibson, 2005) in prompts and generated text. Comparing the >20000 clauses, Grover recreates human word co-occurrence patterns and clause types across discourse modes. However, its coherence relations have shorter length and lower quality, with many nonsensical instances. Therefore, annotators could perfectly guess the human/algorithmic source of documents. Using a corresponding GPT-3 sample, we discuss aspects of generation that have and have not improved since Grover.