Because you can't add geometric figures.
In a triangle, if two sides show to be congruent, you would use the reflexive property of congruence. (AB=AC) A /\ / \ / \B CAs shown in this diagram AB and AC obviously show to be parallel(as shown...
There is not Substitution Property of Congruence. There is, however, one for Equality, called the Substitution Property of Equality (no duh).
The transitive property is if angle A is congruent to angle B and angle B is congruent to angle C, then angle A is congruent to angle C.
Symmetric Property of Congruence: If angle A is congruent to angle B, then angle B is congruent to angle A.