Original title: The Emergence of a Distinction between Things and Stuff
Vivian C. Paulun, Sanghee Song, Elizabeth Spelke · September 2026
Adults know that solid objects stay in one piece, while non-solid stuff, like sand, can split apart. Researchers wanted to find out when babies learn this difference. They tested 4-to-6-month-old and 13-to-15-month-old infants using videos of a solid object or non-solid sand. In the tests, the object or the sand fell onto a wedge. It either split into two pieces or piles, or stayed whole on one side. Babies look longer at things that surprise them. Infants in both age groups looked longer when the solid object split apart. But with sand, they had no preference. They did not expect sand to stay together or split apart. Expectations about how things and stuff hold together develop along different timelines.
At the beach, you drop a rock and a handful of sand. You know the rock will stay in one piece, but the sand will scatter. The hard part is knowing whether a baby who has never seen sand before would expect it to scatter. In this paper, researchers showed babies videos of a solid object and sand to see if they had different expectations.
This matters because it shows that the distinction between solid objects and loose substances is not innate but develops over time. It tells us that babies as young as 4 months expect a block to stay together, but they have no such expectation for sand. This helps us understand how humans build their understanding of the physical world from experience.
The study does not establish when infants develop expectations for non-solid substances, only that they lack them at 15 months. It also only tested sand, so it is unclear if the results apply to other non-solids like water or jelly.
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The Emergence of a Distinction between Things and Stuff — Vivian C. Paulun, Sanghee Song, Elizabeth Spelke — PsyArXiv — doi:10.31234/osf.io/d4cwg_v1
Abstract licence: CC BY
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.