Let \Pi=(P,L) be a partial linear space in which any line contains three
points and let K be a field.
Then by {\cal L}_K(\Pi) we denote the free K-algebra generated by the
elements
of P and subject to the relations xy=0 if x and y are noncollinear
elements from P and xy=z for any triple \{x,y,z\}\in L.
We prove that the algebra {\cal L}_K(\Pi) is a Lie algebra if and only if K is of even
characteristic and \Pi is a cotriangular space satisfying Pasch's axiom.
Moreover, if \Pi is a cotriangular space satisfying Pasch's axiom,
then a connection between derivations of the Lie algebra {\cal L}_K(\Pi)
and geometric hyperplanes of \Pi is used to determine the structure of the
algebra of derivations of {\cal L}_K(\Pi).