1 The main units of derivational analysis

2 Derivational patterns
Both bases and affixes are combined according to a set of rules known as derivational patterns. A derivational patternis a scheme on which words are made up. The pattern consists of two parts: the left and the right. In the left-hand part we have the base and another base or and affix, and in the right-hand part we have the resulting word. E.g.: un/employ/ment – pf + R + sf (morph. pat.); pf + n = N(deriv. pat.)
Morphemically they are the same, but derivationally they are different: the 1^st – suffixal formation, the 2^nd – prefixal formation.
The derivational bases, derivational affixes and derivational patterns are the micro units of the derivational system of the English language; the macro units of this system are the derivational row of words and the derivational cluster. These two units comprise words built on the same or different derivational patterns. 

to father	father	fatherhood	fatherless	fatherly
V	N	N	A	D
-	mother	-	-	-
-	brother	-	-	-

Vertically we have words with the same derivational element (n + less = A); these words are called a derivational row (set):it is a group of words built on the same derivational pattern, the words possess the identical affixal morpheme, the words have the same structural meaning, though each of them has a meaning of its own (in the given example the common derivational meaning – devoid of smth denoted by the base)⁵.

Horizontally we have words containing the same root and built on different patterns; these are the so-called derivational clusters. A derivational cluster (DC) is a complex unity of words possessing the same root-morpheme but built on a number of patterns and characterized by specific organization.
Affixation. Classification of affixes.
Affixation is generally defined as the formation of words by adding derivational affixes to stems. On the morphemic level every word formed by means of affixation has only one root-morpheme, which is its semantic center and one or more derivational affixes. For instance, the word displease has only one root-morpheme and one derivational affix – the prefix dis- . On the derivational level derived words comprise a primary stem, the stem being in itself either a simple, a derived or a compound stem and a derivational affix. For instance, violonist = n + -ist (a simple stem), friendliness = (n + -ly) + -ness (a derived stem), chairmanship = (n + n) + -ship ( a compound stem).
Prefixation is the formation of new words with the help of prefixes. Prefixes are affixes which precede the root. There are about fifty prefixes in Modern English. Prefixes may function in more than one part of speech, prefixes modify the lexical meaning of the stem, but they seldom affect the lexico-grammatical meaning of the word, they don’t change the part of speech of the word.
Prefixes may be classified from synchronical and diachronical approach.
Synchronically prefixes can be classified in different ways.