diff --git a/book/source/06-certifications.md b/book/source/06-certifications.md
index d68bc9b..e030270 100644
--- a/book/source/06-certifications.md
+++ b/book/source/06-certifications.md
@@ -150,6 +150,15 @@ Note: certification signatures [can be made irrevocable](https://www.ietf.org/ar
 
 #### Hard vs. soft revocations
 
+A revocation signature may contain a subpacket indicating the reason for revocation. This subpacket contains a code which specifies why the revocation was issued. This code determines, whether the revocation is hard or soft.
+
+A soft revocation is typically used for graceful or planned revocations. A soft revocation can be reverted by re-validating the certificate, User ID or subkey with a fresh binding signature.
+A soft revocation invalidates the target certificate beginning with the revocations creation time.
+
+Contrary, a hard revocation cannot be re-validated. Furthermore, a hard-revoked certificate is invalidated retroactively.
+
+A missing revocation reason subpacket is equivalent with a hard revocation reason.
+
 ### Certification Recipes
 
 As mentioned above, different signatures are used for different purposes.