diff --git a/01_phonetics/assignment01.md b/01_phonetics/assignment01.md
index e02fcd5..b849bbf 100644
--- a/01_phonetics/assignment01.md
+++ b/01_phonetics/assignment01.md
@@ -14,17 +14,18 @@
 
 **If a language has fewer consonants, will the consonants that it does have be simpler and easier to articulate?**
 
-With their *size principle* @Lindblom-and-Maddieson-1988 suggest a positive correlation between the a language's consonant inventory size and consonant simplicity. 
-A consonant is simpler if it is easier to pronounce and to distinguish from other.
+With their *size principle* @Lindblom-and-Maddieson-1988 suggest a positive correlation between a language's consonant inventory size and consonant simplicity. 
+A consonant is simpler if it is easier to pronounce and to distinguish from others.
 The intuitive explanation for the size principle is kind of a consonant darwinism: 
-If a consonant is hard to pronounce speaker will simplify or even omit them. If a consonant is hard to distinguish of another, they will probably melt together over time. 
-Beside this intuitive explanation we can find a lot of examples in the world's language which support the size principle, small inventories with just simple consonants or complex consonants only in large inventories.  
+If a consonant is hard to pronounce the speaker will simplify or even omit it. If two consonants are hard to distinguish one from the other, they will probably melt together over time. 
+Beside this intuitive explanation we can find a lot of examples in the world's language which support the size principle: small inventories with just simple consonants or complex consonants only in large inventories.  
 
-The *glottalized consonants* require "more intricate coordination of the actions of the larynx with the actions of the articulators in the mouth than many of the more common sounds" [@wals-7] and are therefore not simple or complex consonants. 
-For example the sub group of *ejective stops* require complete closing of the vocal folds and upwards movement of the larynx exacly timed so that the air will be compressed and a explosive noise on opening the mouth apears. [@wals-7] 
-Even there are three different subgroups of glottalized consonants over $70$% of the languages ($409$ out of $567$) have non at all. 
-The amount of complex consonants in the consonant inventory classes mirror perfectly what we expect from the size principe. $66.7$% of the large consonant inventory class ($34$ or more consonants) contain glottalized consonants, but only $8.7$% of the small consonant inventory size class ($6$ to $14$ consonants) do [see @wals-7, Table 2].
+The *glottalized consonants* require "more intricate coordination of the actions of the larynx with the actions of the articulators in the mouth than many of the more common sounds" [@wals-7] and are therefore not simple but complex consonants. 
+For example the sub group of *ejective stops* require an exactly timed complete closing of the vocal folds together with upwards movement of the larynx, so that the air will be compressed and a explosive noise on opening the mouth appears [@wals-7]. 
+Although there are three different subgroups of glottalized consonants, over $70$% of the languages ($409$ out of $567$) have non at all. 
+The amount of complex consonants in the consonant inventory classes mirror perfectly what we expect from the size principle. $66.7$% of the large consonant inventory class ($34$ or more consonants) contain glottalized consonants, but only $8.7$% of the small consonant inventory size class ($6$ to $14$ consonants) do [see @wals-7, Table 2].
 
-**HIER MUSS NOCH EINE CONTRA REFERENCE HIN !!!**
+Lots of data seem to support the size principle. Hard to pronounce glottalized consonants or special consonants like *clicks*, *labial-velar plosives*, *pharyngeals* and *non-sibilant fricatives* are much more likely to find in languages with large consonant inventory [@wals-19]. 
+Consonants in languages with small sized consonant inventory are more likely easy to articulate.
 
 **References**
diff --git a/01_phonetics/references.bib b/01_phonetics/references.bib
index 4137def..b4bac5e 100644
--- a/01_phonetics/references.bib
+++ b/01_phonetics/references.bib
@@ -20,6 +20,17 @@
   year      = {2013}
 }
 
+@inbook{wals-19,
+  address   = {Leipzig},
+  author    = {Ian Maddieson},
+  booktitle = {The World Atlas of Language Structures Online},
+  editor    = {Matthew S. Dryer and Martin Haspelmath},
+  publisher = {Max Planck Institute for Evolutionary Anthropology},
+  title     = {Glottalized Consonants},
+  url       = {http://wals.info/chapter/19},
+  year      = {2013}
+}
+
 @incollection{Lindblom-and-Maddieson-1988,
   address    = {London},
   author     = {Lindblom, Björn and Maddieson, Ian},