Negative Evidence
‘Negative
evidence’ refers to the wrong or ungrammatical expressions. Negative evidence
is a part of Chomsky’s universal grammar theory. According to him the input is
degenerate in the sense that it does not usually contain ’negative evidence’
,information from which the learner could work out what is not possible in a
given language. Speakers proficient in a language know what expressions are
acceptable in their language and what expressions are unacceptable. The key
puzzle is how speakers should come to know the restrictions of their language,
since expressions which violate those restrictions are not present in the
input. This absence of negative evidence—that is, absence of evidence that an
expression is part of a class of the ungrammatical sentences in one's language
proves that a language is not learnable from input only. There are two kinds of
negative evidences such as overt and covert.
Overt
negative evidence is unavailable to a child because caretakers react to the
truth value,not from,of children’s utterances and rarely correct the
ungrammatical speech.Covert negative evidence is also unavailable ,since all
that learners hear is grammatical utterances.
In order to
understand the negative evidence we can study the following two examples:
For example,
in English one cannot relate a question word like 'what' to a predicate within
a relative clause (1):
(1) *What did John meet a man who sold?
Such
expressions are not available to the language learners, because they are, by
hypothesis, ungrammatical for speakers of the local language. Speakers of the
local language do not utter such expressions and note that they are
unacceptable to language learners.
We can also
study the following two sentences to learn about the negative evidence.
1,We gave
the book to the girl.
2,We
explained the answer to the girl.
Apparently
these two sentences have the same surface structures,but whereas (1) contains
an indirect object and can be rewritten as (3),
3,We gave
the girl the book.
(2) contains
a prepositional phrase and cannot be rewritten as (4):
4,We
explained the girl the answer.
How does the
child find out that ’give’ takes an indirect object and ’explain’ a
prepositional phrase?How does the child discover that (4) is ungrammatical?
One possible
answer is that the adults correct the children , but the research does show the
different thing. It seems logical to assume ,therefore , that there must be
some innate principle which prevents the child from producing sentences like
(4).