One of the challenges of discussing validity arguments for machine scoring of essays centers on the absence of a commonly held definition and theory of good writing. At best, the algorithms attempt to measure select attributes of writing and calibrate them against human ratings with the goal of accurate prediction of scores for new essays. Sometimes these attributes are based on the fundamentals of writing (e.g., fluency), but quite often they are based on locally developed rubrics that may be confounded with specific content coverage expectations. This lack of transparency makes it difficult to provide systematic evidence that machine scoring is assessing writing, but slices or correlates of writing performance.