Update gwb_philosophy.md

Corrects typos and grammar.

doc/sphinx/introduction/gwb_philosophy.md

@@ -2,7 +2,7 @@
 GWB philosophy
 ==============
 
-Setting up complex 2D models of geodynamic settings has in the past be hard but feasible. With the advance and the widespread availability of ever more powerful computers to the geodynamic community, detailed regional 3D problems are now within computational range. Although successful attempts have been published, such model setups often have one or many of the following issues:
+Setting up complex 2D models of geodynamic settings has in the past been hard but feasible. With the advance and the widespread availability of ever more powerful computers to the geodynamic community, detailed regional 3D problems are now within computational range. Although successful attempts have been published, such model setups often have one or many of the following issues:
 
 1. Code is not readable (even hard for their developers)
 2. Code/initial conditions is/are not modifiable (even hard for their developers)
@@ -13,11 +13,11 @@ Setting up complex 2D models of geodynamic settings has in the past be hard but
 **The Geodynamic World Builder (GWB) is designed to solve these problems.**
 
 
-To solve these problems, the GWB is build with both a code and a user philosophy in mind. The code philosophy is designed to solve the extendibility, portability and shareability issues and the user philosophy is designed to solve the readability and modifiability issues.
+To solve these problems, the GWB is built with both a code and a user philosophy in mind. The code philosophy is designed to solve the extendibility, portability and shareability issues and the user philosophy is designed to solve the readability and modifiability issues.
 
 ## GWB Code Philosophy
 
-The code philosophy is build around the following points:
+The code philosophy is built around the following points:
 
 1. A single text-based input file
 2. Code, language and platform independent
@@ -32,15 +32,15 @@ Following these points will help to create a clean, portable, extendable code wi
 
 ## GWB User Philosophy
 
-The user philosophy is build around the following points:
+The user philosophy is built around the following points:
 
 1. Tectonic features can be parameterized by lines and area
 2. These features implicitly define a volume 
-3. to which a model can be assigned describing
+3. To which a model can be assigned describing
    1. temperature
    2. composition (a label for a material)
    3. Crystal Preferred Orientation
    4. etc.
 4. Parameterized by a human readable JSON file
 
-The main idea behind these points is design the GWB so that users can easily create complex parameterized initial conditions for their geodynamic setting. How this works should become more clear when reading the rest of the manual.
+The main idea behind these points is to design the GWB so that users can easily create complex parameterized initial conditions for their geodynamic setting. How this works should become more clear when reading the rest of the manual.