What would it mean for an animal to think?
For psychologists who study animal learning, the interesting question is no longer whether animals think but what kind of mental machinery supports their behavior. A useful working definition is that thinking means holding and manipulating mental representations—internal stand-ins for things in the world. On this view, an animal that remembers where food was hidden, or anticipates what a predator will do next, is doing something genuinely cognitive rather than simply running off a reflex [1].
This representational framing matters because it shifts the research focus. Instead of asking whether an animal has a human-like inner monologue, researchers ask whether it can flexibly use and combine its internal representations. That is a question that can be tested experimentally, and it is the focus the field has largely settled on [1].
The hard part: can animal thoughts nest inside each other?
Human thought has a distinctive feature: recursion. A complete sentence can be tucked inside another sentence—under negation, under 'or', or under 'perhaps'—and this can be repeated indefinitely. The mental representations behind those sentences must have the same expressive power, which is why humans can reason about possibilities, impossibilities, and logical connections in a way that seems effortless [4].
Whether nonlinguistic animals have recursive thought is genuinely unresolved. Descartes argued that animal thought lacks this structure, and some contemporary philosophers agree, while others argue that structured representations can exist without language. The question cannot be settled by philosophy alone; it requires empirical studies comparing creatures with and without language [4].
One promising route is developmental: trace how human children acquire recursive language and see which cognitive abilities arrive alongside it. Work on children's grasp of possibility concepts—words like 'might' and 'maybe'—shows that many three-year-olds represent a single possible outcome without marking it as merely one option among several, and only later do they deploy full possibility concepts. The trajectory is gradual: no two-year-olds, about 20% of three-year-olds, and perhaps half of four-year-olds show the full concept in problem solving [4]. Because young children lack these concepts for a while, the same logical operator may also be unavailable to nonlinguistic animal thought—a hypothesis the dissertation leaves open rather than settles [4].
Why the boundary between human and animal minds has been drawn so firmly
The idea that animals cannot truly think has deep historical roots. In thirteenth-century Paris, theologians agreed that animals lacked a rational soul, and they worked hard to explain animal behavior—a sheep fearing all wolves, ants storing grain—without granting animals free will, abstract concepts, or the ability to form universal categories. Albert the Great described the ant's foresight as only 'a sort of prudence,' not genuine abstract reasoning [5].
These thinkers did allow limited exceptions. Alexander of Hales permitted a restricted kind of 'animal thinking' about God, confined to sensory things, and some theologians acknowledged likenesses between human and animal behavior even while keeping the fundamental divide intact [5]. The historical record is more heterogeneous than a simple 'animals don't think' story suggests, but the shared starting assumption—animal irrationality—shaped what counted as an explanation for centuries [5].
Early modern writing shows a similar plurality. Medical and philosophical tracts usually treated animal sentience abstractly, as a foil for what made humans special, while hunting books, husbandry books, and natural histories engaged with animal intelligence only as far as practical human interests required. Literary works such as Cervantes's could portray select animals as emotional, intentional, and sometimes inscrutable, offering a fictional model of embodied animal minds rather than a scientific claim [3].
Why the answer matters beyond the lab
How animals think is not only a scientific puzzle; it bears directly on animal welfare. Researchers and ethicists interviewed on the topic frame welfare around how animals feel and think, which means assumptions about animal cognition feed into decisions about how they should be treated [2]. If animals form and manipulate representations, the case for taking their mental lives seriously becomes harder to dismiss.
What remains genuinely open is the recursive question. The evidence supports representation and manipulation of mental content in animals, and it leaves open whether their thoughts have the nested, language-like structure that lets humans reason about incompatible possibilities at once [1][4]. That is the frontier the field is still working toward, and it is a question that empirical studies of both children and nonlinguistic animals will have to answer [4].
Sources used in this answer
Can animals think?
The paper reviews psychological perspectives on animal thought and argues that a consensus has emerged that animals can think, with the capacity to manipulate mental representations as a convenient research focus.
How animals feel and think
The paper examines animal welfare through interviews, focusing on how animals feel and think as a basis for understanding their cognitive and mental lives.
Human Thinking about Thinking Animals in the Early Modern Spanish and Spanish American World
The paper analyzes early modern Spanish and Spanish American sources, showing a plurality of views on animal cognition and sentience, with Cervantes portraying select animals as emotional, intentional, and sometimes inscrutable.
The wisdom of "might": How children come to know what possibilities are
The paper explores how children acquire possibility concepts and argues that whether recursive operations structure the thoughts of nonlinguistic animals remains an open empirical question.
Thinking about Animals in Thirteenth-Century Paris: Theologians on the Boundary between Humans and Animals
The paper analyzes thirteenth-century Parisian theologians who agreed animals lack a rational soul and explained animal behavior without granting them free will, abstract concepts, or universal categories, while allowing limited likenesses between human and animal behavior.