Expressions and Syntax: Objects and Fcurves Expressions are formulas that replace the actions of a Function Curve (Fcurve). An expression can ONLY be applied to an existing Fcurve of an object. Each object in your scene may therefore have a maximum number of expressions on it equal to the number of Fcurves it has. For example, on a primitive object I can have one expression on the explicit translation in X, another completely different expression on explicit translation in Y, another on scale in Z, and so on, until I run out of Fcurves. When an object has an expression applied to an Fcurve, no manual changes may be made to that property. For instance, when I apply an expression to a gear that controls the rotation in Z, I cannot manually rotate the gear in Z anymore - the expression has taken over control of the rotation in Z Fcurve. Expressions are most often applied to geometry objects in your scene, but you can also write expressions to control other objects, like lights, materials, textures, and the camera. For instance, if you wished to apply an expression to the diffuse color of a ball so that it changed color when it hit the floor, you would select the Material node of the ball in the Schematic view, and apply the expression to that node, not to the object itself. Expression use the names of the Fcurves to describe properties in the equation. These names are the same you have seen in the list of present Fcurves at the top right corner of the Fcurve window. The most commonly used are listed below. trans : The Translation Fcurve specifies the location of an object on a path, from 0% to 100%. etrnx : The Explicit Translation in X Fcurve specifies the location of the object in the X axis. etrny : The Explicit Translation in Y Fcurve specifies the location of the object in the Y axis. etrnz : The Explicit Translation in Z Fcurve specifies the location of the object in the Z axis. scalx : The Scale in X Fcurve scales the object in that axis. scaly : The Scale in Y Fcurve scales the object in that axis. scalz : The Scale in Z Fcurve scales the object in that axis. rotx : The rotation in X Fcurve rotates the object around the X axis of the object center. roty : The rotation in Y Fcurve rotates the object around the Y axis of the object center. rotz : The rotation in Z Fcurve rotates the object around the Z axis of the object center. For a complete list of the Fcurves available for your use on a specific object, open the Fcurve editor and click the Fcurve button to see a list.