  In every variety of algebras $\Theta$ we can consider its logic and its
algebraic geometry. In the previous papers geometry in equational logic, i.e.,
equational geometry has been studied. Here we describe an extension of this
theory towards the First Order Logic (FOL). The algebraic sets in this geometry
are determined by arbitrary sets of FOL formulas. The principal motivation of
such generalization lies in the area of applications to knowledge science.
  In this paper the FOL formulae are considered in the context of algebraic
logic.
  With this aim we define special Halmos categories. These categories in the
algebraic geometry related to FOL play the same role as the category of free
algebras $\Theta^0$ play in the equational algebraic geometry.
  The paper consists of three parts. Section 1 is of introductory character.
The first part (sections 2--4) contains background on algebraic logic in the
given variety of algebras $\Theta$. The second part is devoted to algebraic
geometry related to FOL (sections 5--7). In the last part (sections 8--9) we
consider applications of the previous material to knowledge science.
