English several morphemes but the boundaries between them

English is regarded as fairly mixed type of language in respect of the
three types of isolating, agglutinative and inflecting language because it
simply contains characteristics of all three.

In English language we can find isolating examples such as most of
adverbs, prepositions or conjunctions (since, to, from, when, at). Most of them
contain only one morpheme which matches the rules. Their grammatical status is completely determined
by their relations with the rest of the sentences in which they appear. It is nearly impossible for those to appear by their own and have a
significant meaning.

We can also
notice agglutination in the English language which proves that English is also
an agglutinative language. We add to the word in order to add to its meaning as
well. A great example might be adjectives. We usually add to the word and
change its role in a sentence (ugly – ugliness, dark – darkness). In an agglutinating language, a word may
consist of several morphemes but the boundaries between them are clear-cut.

Finally,
coming to the last of three types of languages that can be found in English – “fusional
languages” or “inflected languages” which are a distinguished from “agglutinative”
languages by their tendency to use a
single inflectional morpheme to stand for multiple grammatical, syntactic, or
semantic features. There is no clear distinction between a root of the word
and the word created itself, however it is not impossible to associate the
original word with the changed one. A great example of fusion in English might
be tenses, like “rise, rose, risen”, where the basic meaning stays the same,
nevertheless the word presents three different tenses which plays a big role in
language usage and sentence creation.

To sum up
briefly. There are three main groups
of languages based on structural grounds: 
isolating (called analytic as well), agglutinative and fusional
(inflecting). Each type can be found in
English language, however none of those can be distinguished as a main type.
There are different characteristics of each type. In fusional languages we are unable to distinguish clear boundaries between morphemes,
in the isolating languages the
syntactic relations are expressed by the position of the words in the sentence
and the words are usually short consisting of low number of morphemes, and in agglutinating
languages morpheme has an regular shape which makes it easy to identify.