Jeder/jede/jedes/jeden are the case declensions for the adjective ,'jeder' in Nominative case(subject) and Accusative cases (direct object)
Jeder means ,'every' in English, in nominative case jeder will be ,
1. 'Jeder' with the masculine subject 2. 'Jede' with the Feminine subject 3. 'Jedes' with the neuter subject 4. 'Alle' to be usedfor plural , for the plural meaning 'all'
In Accusative case,
1, 'Jeden' with the masculine object 2. 'Jede' with the Feminine object 3. 'Jedes' with the neuter object 4. 'Alle' to be used for plural
There are two more cases, Dative(Indirect Object) and Genitive which i have not detailed.
This is where I nearly quit learning German. Gender and case change many words in a sentence. As far as I know, the proper ending for the definite article "jede" is dictated by the case and gender of the proceeding noun. Definite article endings (strong) Masculine Neuter Feminine Plural Nominative -er -es -e -e Accusative -en -es -e -e Dative -em -em -er -en Genitive -es -es -er -er
I think it's because the book is being read - it becomes the 'accusative' subject. He is doing something to the book - i.e. reading it. A bit like earlier when the tuition was around eating apples, 'Er isst den Apfel' the 'den' being used as the apple was being eaten rather than 'der' that is the normal gender term.
This link will help you much http://deutsch.lingolia.com/en/grammar/adjectives/declension.
Hsving read this: http://www.netplaces.com/german/the-good-the-bad-and-the-ugly/der-words-and-ein-words.htm, I could say it's the difference between "der words" and "ein words". Jeder and mein belong to those groups respectively.
This article may be helpful: https://yourdailygerman.wordpress.com/2014/02/03/german-adjective-endings-3/
If you had a choice between ten books, and you said "I'll read any of them" it means any book is fine with you, not necesssarily that you read every book. Perhaps you just want to read a book, and do not care which. But reading every book would mean all 10 books are to be read
I feel confident with this link, please use this link often http://deutsch.lingolia.com/en/grammar/adjectives/declension.
Definite article -> der der Apfel Indefinite article -> ein ein Apfle No article Apfel
"He reads every book": Er liest jedes Buch
"He reads all books": Er liest alle Bücher (note the plural makes it a less direct translation)
"He reads all the books": Er liest alle die Bücher
"He reads all of the books": Er liest alle der Bücher (genitive case for "of the books", possibly not used much)
Just as with English, there are different sentence structures that mean the same thing. Where it makes sense to do so, you should keep the same sentence structure when translating.