Dualism

Thomas is neither a materialist, the real including spiritual substances (God, the angels, the intellective soul), nor an idealist, the sensible world having a consistency of its own. His position approaches a moderate dualism: the human creature is composed of a material body and a subsistent spiritual soul, but this dualism is tempered by the hylomorphic unity, which refuses to treat the human being as two juxtaposed substances, as Descartes later would.

Summa Theologiae, Ia, q. 75-76

Locke admits a bodily reality endowed with primary qualities (extension, figure, motion) that our ideas copy, but also a thinking mind; and he confesses he cannot know whether God might not have given matter the power to think. This cautious dualism of body and mind, alongside a solid realism of bodies, rules out both idealism and strict materialism, hence weights shared between materialism and dualism.

Essay Concerning Human Understanding, II, ch. 8 (primary and secondary qualities) and IV, ch. 3, §6 (thinking matter)

Beauvoir elaborates no systematic metaphysics, but her existentialist-inflected phenomenology presupposes a primary material and bodily reality, grasped through the consciousness that gives it meaning. The body, neither pure thing nor pure idea, is lived as situation, which forbids ranging her squarely under materialism or idealism.

The Second Sex (1949), "The Data of Biology" and the body as situation

The ontology of Being and Nothingness sets two regions of being against each other: the in-itself, full, opaque, what it is, and the for-itself, consciousness, a nothingness that brings forth the world and its meanings. This is not a substance dualism in Descartes's manner, since the for-itself is no thinking thing but a fissure in being; nor is it a materialism, consciousness not being reducible to the in-itself. The position stands between a basis of brute being and the irreducibility of conscious upsurge, hence the shared weights.

Being and Nothingness, Introduction (the in-itself and the for-itself)

Hume suspends every strong thesis about the ultimate nature of the real: he treats as a fiction both the belief in the continued, independent existence of bodies and the belief in a spiritual substance, without denying either in ordinary life. This skepticism about substance, material or immaterial, forbids any clear classification and yields near-balanced weights, with a slight tilt toward the dualist doubt inherited from his examination of perceptions.

A Treatise of Human Nature, I, part IV, sect. 2 (of scepticism with regard to the senses) · A Treatise of Human Nature, I, part IV, sect. 5 (of the immateriality of the soul)

Spinoza is a monist: a single substance, God or Nature, of which thought and extension are two attributes expressing the same reality under two aspects (the order and connection of ideas is the same as the order and connection of things). His position therefore fits none of the three slots: it stands at the centre, neither materialist (extension is not primary) nor idealist (nor is thought), and its dualism of attributes is not a dualism of two substances. Hence near-equal weights.

Ethics, II, prop. 7 (parallelism of ideas and things) · Ethics, I, def. 4 and prop. 14 (the attributes of the single substance)