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This function helps the Soul to carry out the operation of “Knowing”.

Immaterial Cognition

This is source of intellect’s power to know universals, abstract truths, and immaterial realities.

Immaterial cognition consists of reasoning and understanding the immaterial aspects of material form, and it reduces material reality to its simplest principles: unity in quantity and point in space, neither of which exists materially, yet both are necessary for understanding number and shape.

In immaterial cognition, the intellect grasps chair-ness as a fundamental abstract, the simplest principle by which any object is recognized as something meant for sitting. When we think of a specific instance, such as an office chair, the mind forms a mental image, which is a concrete abstract derived from imagination or from experience and accessed through memory. From this, rationalization develops comprehensive abstraction by organizing chairs according to function (dining, recliner, office), structure (four-legged, cantilever, rocking, folding), and material (wood, metal, plastic, upholstered), while also generating new designs through imagination that aim to realize chair-ness in specific and practical forms.

Similarly, in immaterial cognition, the intellect grasps tent-ness as a fundamental abstract, the simplest principle by which any structure is recognized as a temporary shelter. When we think of a specific instance, the mind forms a mental image, which is a concrete abstract derived from memory or imagination. From this, rationalization develops comprehensive abstraction by organizing tents according to function, structure, and material, and also rationalization generates new designs through imagination, each aiming to realize tent-ness in specific and practical forms.

In simple words: Immaterial cognition is thinking, understanding, and reasoning about things that are not physical, like ideas, meanings, truth, and general concepts.

Rationalization

An act of the intellect (of the soul not of the brain), where it reasons from one truth to another, using images provided by the brain.

Through rationalization (discursive reasoning), the soul’s intellect forms comprehensive abstract notions by relating fundamental abstract notions.

Rationalization develops mathematics and geometry from fundamental abstract notions such as “1” and “point,” respectively.

This means that once the soul’s intellect has grasped basic universal ideas—such as one, point, it can actively relate them to one another to build richer and more detailed concepts. For example, from the fundamental abstract notion of one, the soul’s intellect forms 2, 3, 4, .... by understanding repeated oneness, and from these arise arithmetic operations such as addition, subtraction, multiplication, and division, which are comprehensive abstract notions expressing relations between numbers rather than mere collections of objects. Similarly, from the fundamental abstract notion of a point, which has no size or shape, the soul’s intellect forms lines by understanding ordered points, two-dimensional shapes such as squares and circles by relating lines, and three-dimensional shapes such as cubes and spheres by relating surfaces. These are not directly given by the senses, but are intelligible structures formed by reason.

Examples

More day to day examples:

Chairs: Organized by function (dining, recliner, office), structure (four-legged, cantilever, rocking, folding), and material (wood, metal, plastic, upholstered), while also generating new designs that aim to realize “chair-ness” in practical forms.

Tents: Organized by function, structure, and material, while also generating new designs that aim to realize “tent-ness” in specific and practical forms.

In simple words: Rationalization is thinking, understanding, and reasoning using both physical images (from the brain) and non-physical meanings (by the intellect).

Material Cognition

Material cognition is the level where the soul operates through the brain and body, using sensory input and neural processing. Mechanically, this begins with the senses taking in data—sight, sound, touch—after which the brain converts these into electrical and chemical signals. These signals are processed into images, memories, and associations. The mind at this level does not “know” in the immaterial sense. The mechanics are: input (senses) → encoding (neural signals) → storage (memory) → recall and association → response (emotion, impulse, or action tendency). This is why this level is called material cognition—it depends on physical structures and processes, even though the soul uses them as instruments.

The brain’s sensory operations: perception, imagination, memory, and image-processing.

The (lower) cognitive or sensory-cognitive function of the brain carries out material operations such as imagination, memory, phantasia, sensory recognition, association, and image-based processing.

Key Operations

1. Imagination (phantasia) — forming and manipulating internal images.
2. Memory (memorativa) — retaining and recalling sensory images.
3. Phantasia — refining, combining, and recombining images.
4. Sensory Recognition — identifying what an image represents.
5. Association — linking images, patterns, and experiences.
6. Cogitative Power (particular reason) — making instinctive judgments about particulars.
7. Discursive Image-Based Processing — step-by-step processing that depends on images.

These operations are material, sensory-based forms of “thinking,” but they are not true intellectual reasoning.

The brain performs lower-level logical processing—such as pattern comparison, association, and sensory-based inference. However, true logical reasoning, which operates on universals and abstract concepts, belongs exclusively to the soul’s immaterial intellect.

Note: Imagination vs Phantasia

Imagination is a single internal sense power that produces and manipulates images.

Phantasia refers to the broader sensory-image system—formed by imagination, memory, recognition, and association—from which the intellect abstracts universal knowledge.

In simple words: Material cognition is thinking, understanding, and processing things that are physical, like images, sounds, memories, and sensory experiences.

1. Imagination (phantasia) — forming and manipulating internal images. 2. Memory (memorativa) — retaining and recalling sensory images. 3. Phantasia — refining, combining, and recombining images. 4. Sensory Recognition — identifying what an image represents. 5. Association — linking images, patterns, and experiences. 6. Cogitative Power (particular reason) — making instinctive judgments about particulars. 7. Discursive Image-Based Reasoning — step-by-step reasoning that still depends on images. The 7 operations above are material, sensory-based “thinking,” but not true intellectual reasoning. The brain carries out lower-level, material logical processing—such as pattern-comparison, association, and sensory-based inference—but true logical reasoning, which operates on universals and abstract concepts, belongs exclusively to the soul’s immaterial intellect. Note: Imagination vs Phantasia Imagination is a single internal sense power that produces and manipulates images. Phantasia is the full sensory-image system—formed by imagination, memory, recognition, and association—from which the intellect abstracts universal knowledge. Note: Aquinas uses “image” to mean any sensory representation, including sound, smell, taste, and touch—not only visual pictures. According to St. Aquinas, the soul and the mind collaborate to perform an important function called “rationalization.” Definition of rationalization according to St. Aquinas: Rationalization involves the back and forth of argument, moving from one thing known to another, and advancing in knowledge by such movement. The diagram below is a visual representation of how the soul and the brain interact to perform the function of rationalization. The left circle represents immaterial cognition, which is a faculty of the soul. The right circle represents intellectual activities of the brain, such as reasoning, logic, imagination, thinking, and memory. The overlapping area represents the collaborative process called rationalization, where both soul and brain work together. The cursive bracket pointing to intellect might suggest that intellect is a combination of immaterial cognition, rationalization and brain or combination of brain and soul.

Clarification on Soul and Brain (St. Thomas Aquinas)

St. Aquinas strictly rejects the idea of a combination in the following sense:

• Brain + Soul
• Material + Immaterial

The diagram may suggest this at first glance, but that is not the intended meaning.

Rather, the diagram expresses that the soul cooperates with the brain. The soul uses the brain to obtain sensory data, without which it cannot exercise its intellectual powers of thinking and reasoning.

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Without the soul, the brain can:

• Store memories
• Process images
• Compare patterns
• Control signals
• Coordinate the body

However, it cannot understand:

• Universals
• Abstract essences
• Meaning
• Truth
• Laws
• Non-physical concepts

Without the soul, the brain functions like an empty computer—able to process signals, but incapable of intellect, understanding, or rational thought.

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The Operation of the Soul

The operation of the soul through the intellect is “knowing”, which consists of:

• Understanding truth
• Judging truth
• Reasoning from one truth to another

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How the Soul and Brain Cooperate

The cooperation happens in the following order:

1. Senses receive data
   • Eyes, ears, touch, etc.
   • Images, memories, sensory maps

   (ST I, q.84)

2. Brain forms phantasms

   Aquinas teaches that the intellect cannot think without phantasms (mental images).

   • Sensory memories
   • Images
   • Imagination
   • Emotional coloring
   • Pattern recognition
   • Attention and coordination

   (ST I, q.84, a.7)

3. Intellect abstracts a universal idea

   Immaterial Cognition: The intellect can know:

   • Universals (humanity, triangularity, justice)
   • Example: From many circles, it understands “circularity”
   • Immaterial realities (truth, laws, mathematics)
   • Meanings, not just sensory shapes

   This is called immaterial cognition because:

   • It is not limited by physical matter
   • Its objects are not material
   • It understands abstract form

   (ST I, q.85, a.1)

4. Intellect forms judgments

   “This is true” / “This is false”

5. Rationalization (Reasoning)

   Argument, conclusion, decision.

   Rationalization = the intellect performing higher operations:

   • Simple apprehension – forming a concept
   • Judgment – determining truth or falsehood
   • Reasoning – moving from premises to conclusion

   (ST I, q.85, a.2–3)

   → Rationalization is an immaterial act of the intellect.
   → It does not belong to the brain, but uses the brain’s data.

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Conclusion

Thus:

• The brain supplies the matter
• The intellect supplies the form

As said earlier, the intellect, as a function of the soul, produces knowledge by enabling the act of knowing. This act of knowing has a clear purpose: it is directed toward discovering and understanding truth. When we know something in this sense, we are not merely aware of it or familiar with it, but we grasp what it is and why it is so. The human intellect comes to know the truth about anything by forming and using ideas, or notions, that are not physical objects themselves but help us understand physical and non-physical things. Human understanding works through different levels of ideas, which we can call fundamental abstract notions, comprehensive abstract notions, and concrete notions. These levels explain how we come to know the truth about things—not by storing every idea as a finished object, but by understanding relations when we actively think. Fundamental Abstract Notions: At the most basic level are fundamental abstract notions. These are the simplest ideas the intellect can use, such as the concept of 1, which expresses unity, distinction, and countability, or the concept of a point, which is something that has a position but no size. These ideas are not stored in the brain as pictures or sentences. Instead, the intellect retains them as stable abilities or capacities to understand when needed. This is possible because the intellect operates through immaterial cognition, meaning it can grasp ideas that are not physical or image-like. Example: Matter (quantity), Appearance (color), aesthetic (ergonomic) Comprehensive Abstract Notions: Using this basic level, the intellect understands comprehensive abstract notions, which are more organized and structured ideas formed from fundamental ones. These include scientific principles, mathematical relationships, and general explanations about how things work. Such notions are not tied to a single object or situation but apply across many cases. A clear example is found in geometric triangles. Triangularity is commonly described using words in this way: a triangle is a shape formed by three points connected by three straight lines, creating three angles. This description contains words such as point, line, and angle, which are stored in the brain as language and memory, along with many mental images of different kinds of triangles. However, these words and images do not themselves contain triangularity as a universal idea. When the intellect thinks about triangles, the stored images and descriptions—especially the use of the word point (and even words like line and angle, which depend on points)—invoke the fundamental abstract notion of point already habited in the intellect. Through the intellect’s process of rationalization, it reasons about how points are connected and ordered, and in doing so understands what makes something a line, an angle, and eventually a triangle. In this way, triangularity is understood in the act of reasoning, not stored as a separate permanent concept in the intellect, unlike fundamental abstract notions such as point, which are retained as stable capacities to understand. Concrete Notions: At the level of concrete notions, the brain’s powers—such as imagination and memory—work together with the intellect to apply understanding in real situations. At this level, knowledge is closely connected to experience, images, symbols, and practical activity. For example, the fundamental abstract notion of point leads, through the intellect’s process of rationalization, to comprehensive abstract notions of geometric shapes such as line, triangle, and circle. These, in turn, support concrete fields such as mathematical geometry, engineering drawing, architecture, and design. Here, understanding is closely tied to diagrams, symbols, tools, and practical use. Even so, this practical understanding still depends on deeper intellectual principles. It is important to remember that, although memory and imagination belong to the brain, they do not operate independently. The intellect and will of the soul are the primary driving forces that guide and direct the brain’s memory and imagination, allowing concrete knowledge to be formed from fundamental abstract notions and comprehensive abstract notions, and then applied in a meaningful, purposeful way rather than in a purely mechanical manner. Taken together, these three levels show how human understanding works as a living process. The brain stores words, descriptions, and images, while the intellect uses them to activate its deepest abilities. Fundamental abstract notions such as point make understanding possible; comprehensive abstract notions—such as geometric shapes—arise through reasoning; and concrete notions allow us to recognize and apply these ideas in mathematics, engineering, and everyday life. In this way, the intellect comes to know truth—not by passively storing ideas, but by actively understanding relations whenever it thinks.

Introduction

The human soul possesses powers such as intellect and will. These allow humans to know truth and freely choose actions.

Unlike artificial systems, the soul enables true consciousness.