Hossein Jorjani
First publication: 2026 – 07 – 19
The distinction between simplicus and compositum, originally introduced to characterize different kinds of theoretical models, may be generalized into a broader methodological principle applicable to scientific inquiry.
A simplicus object is one whose behavior can be adequately understood at a single level of organization. Its explanation does not essentially depend upon interactions among constituent parts or upon reciprocal relations between parts and wholes. Many elementary scientific models deliberately adopt this character by isolating a limited number of variables, thereby making fundamental principles easier to understand.
A compositum, by contrast, derives its properties from the organization and interaction of its constituent elements. The whole cannot be understood independently of the parts, nor the parts independently of the whole. Biological organisms, ecosystems, economies, languages, societies, and many technological systems exemplify this form of organization.
The distinction applies not only to phenomena but also to observations and measurements. Classical empiricism often treated observations as primitive units of evidence. Modern scientific practice increasingly relies on observations that are themselves products of multiple stages of measurement, calibration, preprocessing, quality control, statistical adjustment, and computational analysis. Such observations are better understood as compositum than as simplicus.
DNA sequencing illustrates this development. A reported genotype is not a direct observation but the result of signal detection, base calling, sequence alignment, genotype calling, quality filtering, and statistical evaluation. Likewise, traits that appear straightforward—such as standardized milk yield in quantitative genetics—may represent the outcome of complex procedures involving editing, extrapolation, standardization, and model-based adjustment. In such cases, the reported observation is itself a structured construction rather than an elementary datum.
The distinction likewise applies to scientific models. Some describe relatively isolated variables, whereas others seek to represent systems whose behavior emerges from multiple interacting levels of organization.
These three domains—phenomena, observations, and models—are logically independent. A relatively simple phenomenon may require highly composite measurements, while a complex phenomenon may sometimes be investigated through comparatively simple observations. Likewise, a sophisticated model may be applied to a relatively simple object, whereas an oversimplified model may be imposed upon a highly structured reality. [1]
The distinction between simplicus and compositum therefore concerns neither difficulty nor sophistication. Rather, it concerns the extent to which understanding depends upon the organization and interaction of constituent elements.
A practical consequence follows from this distinction. Before selecting a scientific method or explanatory framework, it may be useful first to ask whether the object of inquiry is fundamentally simplicus or compositum. Different kinds of objects may require different forms of explanation, different measurement strategies, and different modes of inference.
Whether this distinction can serve as a general organizing principle across the natural and social sciences remains an open question.
[1] The following anecdote illustrates the point. During the early adoption of SNP-chip genotyping, I asked a laboratory researcher how the laser measurements were calibrated before genotype calls were produced. After several attempts to explain what I meant, he finally replied, “I don’t know. The machine takes care of it.” The remark was revealing. From the user’s perspective, the genotype appeared to be a direct observation. In reality, it was the endpoint of a complex sequence of physical measurements, calibration procedures, signal processing, statistical algorithms, and quality-control steps. What was treated as an observation had already undergone extensive inferential processing. The episode illustrates how many modern scientific observations are better understood as compositum than as simplicus.
Hossein Jorjani 