Rationalism holds that reason, rather than sensory experience, is the primary source of knowledge. Key rationalist philosophers include Descartes, who believed that clear and distinct ideas derived through reason are certain, while sensory experiences could be deceiving. He argued that we can understand concepts like polygons through reasoning rather than just senses. Later rationalists like Pythagoras, Plato, and Aristotle emphasized using logic and reasoning to derive truths. In architecture, rationalism sees the field as a science that can be understood through rational principles, as first proposed by Vitruvius. It was an influential movement in early 20th century Italy and again in the late 1960s.

1. Rationalism

2. Comparison – Rationalism & Empiricism

3. Rationalism
EPISTEMOLOGY: Scottish philosopher James Frederick Ferrier to describe
the branch of philosophy concerned with the nature and scope of knowledge.
RATIONALISM: By contrast with empiricism and idealism, which centres around
the epistemologically privileged status of sense data (empirical) and the primacy
of Reason (theoretical) respectively, modern rationalism adds a third 'system of
thinking‘.
IDEA
Source of Knowledge
Justification of our
Knowledge
Source of Conceptual
Apparatus
(1596 -1650)
Father of
Modern
Philosophy

4. René
Descartes
• Never accept anything except clear and distinct
ideas.
• Divide each problem into as many parts are needed
to solve it.
• Order your thoughts from the simple to the
complex.
• Always check thoroughly for oversights.
"Cogito, ergo sum"
Sensations and Passions
Makes several
observations
about mind-
body relation
Primary seat Is
pineal gland
Soul makes a
human body
truly human
“primary seat”,
i.e., the place
where the soul
performs its
primary functions
All sensations
depend on the
nerves
Animal spirits:
Present in tube-
like membranes
CASE STUDY
His last published
work, Passions of the
Soul
provides accounts of how various motions in the body
cause sensations and passions to arise in the soul.

5. Rationalism – Thinkers (Post – modern)
Pythagoras (570–495 BCE) Plato (427–347 BCE) Aristotle (384–322 BCE)
Pythagoras was one of
the first Western
philosophers to stress
rationalist insight. He
summed up the implied
metaphysical rationalism
in the words "All is number
Plato also held
rational insight to a
very high standard,
as is seen in his
works such
as Meno and The
Republic.
Aristotle's great
contribution to rationalist
thinking comes from his
use of syllogistic logic.

6. CASE STUDY 1 - Rationalism
How do we come to know objects, through the senses or through reason?
Descartes brought some of the strongest arguments to believe that the latter option is
the correct one.
CONSIDER POLYGONS
How do we come to recognize features of polygons. The senses here may seem to play
a key role.
But, now imagine to have two figures in front of you, the first with a thousand sides and
the other with a thousand and one sides. Which is which? Well, presumably the senses
will not suffice in providing an answer to this question: you will need reasoning (e.g.
counting) in order to tell them apart.

7. CASE STUDY 2 – Rationalism in Architecture
1. In architecture, rationalism is an architectural
current which mostly developed from Italy in the
1920s-1930s.
2. Vitruvius had claimed in his work De
Architectura that architecture is a science that
can be comprehended rationally. This
formulation was taken up and further developed
in the architectural treatises of the Renaissance.
3. The term structural rationalism most often
refers to a 19th-century French movement,
usually associated with the theorists Eugène
Viollet-le-Duc and Auguste Choisy.
Teatro Carlo
Felice,
designed
by Aldo
Rossi, who is
considered
the founder
of neo-
rationalism
In the late 1960s, a new rationalist movement
emerged in architecture, claiming inspiration from both
the Enlightenment and early-20th century
rationalists.
The former
Casa del
Fascio
in Como, Italy,
designed
by Giuseppe
Terragni.