Simple Sentence a simple sentence consists of just one independent clause: Mary had a little lamb. Compound Sentence

90. CONVERSION, ITS ORIGN AND BASIS
onversion (zero derivation, root formation, functional change) is the process of coining a new word in a different part of speech and with different distribution characteristics but without adding any derivative element, so that the basic form of the original and the basic form of derived words are homonymous. This phenomenon can be illustrated by the following cases: work – to work, love – to love, water – to water.
If we regard these words from the angle of their morphemic structure, we see that they are root words. On the derivational level, however, one of them should be referred to a derived word, as having the same root morpheme they belong to different parts of speech. Consequently the question arises here: “What serves as the word-building means in such cases?” It would appear that the noun is formed from the verb (or vice versa) without any morphological change, but if we probe deeper into the matter, we inevitably come to the conclusion that the two words differ only in the paradigm. Thus, it is the paradigm that is used as a word-building means. Hence, we can define conversion as the formation of a new word through changes in its paradigm.
The change of the paradigm is the only word-building means of conversion. As the paradigm is a morphological category, conversion can be described as a morphological way of forming words.
As a type of word-formation conversion exists in many languages. What is specific for the English vocabulary is not its mere presence, but its intense development.
The main reason for the widespread development of conversion in present-day English is no doubt the absence of morphological elements serving as classifying signals, or, in other words, of formal signs marking the part of speech to which the word belongs. The fact that the sound pattern does not show to what part of speech the word belongs may be illustrated by the word back. It may be a noun, a verb, an adjective, an adverb.
Many affixes are homonymous and therefore the general sound pattern does not contain any information as to the possible part of speech.
e.g.: maiden (N), darken (V), woollen (A), often (Adv).
O. Jesperson points out that the causes that made conversion so widely spread are to be approached diachronically. The noun and verb have become identical in form firstly as a result of the loss of endings. More rarely it is the prefix that is lost (mind < gemynd). When endings had disappeared phonetical development resulted in the merging of sound forms for both elements of these pairs.
e.g.: OE carian (verb) and caru (noun) merged into care (verb, noun); OE drinkan (verb) and drinca, drinc (noun) merged into drink (verb, noun).
A similar homonymy resulted in the borrowing from French of pairs of words of the same root but belonging in French to different parts of speech. These words lost their affixes and became phonetically identical in the process of assimilation.
Prof. A. Smirnitsky is of the opinion that on a synchronic level there is no difference in correlation between such cases as listed above, i.e. words originally differentiated by affixes and later becoming homonymous after the loss of endings (sleep – noun :: sleep – verb) and those formed by conversion (pencil – noun :: pencil – verb).
Prof. I. Arnold is of the opinion that prof. Smirnitsky is mistaken. His mistake is in the wish to call both cases conversion, which is illogical if he, or any of his followers, accepts the definition of conversion as a word-building process which implies the diachronistic approach. Prof. I. Arnold states that synchronically both types sleep (noun) – sleep (verb) and pencil (noun) – pencil (verb) must be treated together as cases of patterned homonymy. But it is essential to differentiate the cases of conversion and treat them separately when the study is diachronistic.