'Synthetic geometry' is the branch of
geometry which makes use of
theorems and synthetic observations to draw conclusions, as opposed to
analytic geometry which uses
algebra to perform geometric computations and solve problems.
The geometry of
Euclid was indeed synthetic, though not all of the books covered topics of ''pure geometry''. The heyday of synthetic geometry can be considered to have been the
19th century; when methods based on
coordinates and
calculus were ignored by some
geometer such as
Jakob Steiner, in favour of a synthetic development of
projective geometry.
For example, the treatment of the
projective plane starting from axioms of incidence is actually a broader theory (with more
models) than is found by starting with a
vector space of dimension three. The close axiomatic study of
Euclidean geometry led to the discovery of
non-Euclidean geometry.
If the axiom set is not
categorical (so that there is more than one model) one has the geometry/geometries debate to settle. That's not a serious issue for a modern axiomatic mathematician, since the implication of
axiom is now ''starting point for theory'' rather than ''self-evident plank in platform based on intuition''. And since the
Erlangen program of Klein the geometrical nature of ''a'' geometry has been seen as the connection of
symmetry and the content of propositions, rather than the style of development.
In relation with
computational geometry, a 'computational synthetic geometry' has been founded, having close connection, for example, with
matroid theory.
Synthetic differential geometry is an application of
topos theory to the foundations of
differentiable manifold theory.