inguists study in comparative historical linguistics?
Comparative historical linguistics: Linguists can study and compare a single language during the time to find out about how they had changed. Or they compare two or several different but related languages to find their proto-language.

2. What do linguists study in comparative typological linguistics?
Comparative typological linguistics: Linguists compare different languages so they will be able to divide the languages into different groups.

3. What is Contrastive Analysis Hypothesis (CAH)?
“individuals tend to transfer the forms and meaning and the distribution of forms and meanings of their native language and culture to the foreign language and culture, both productively when attempting to speak the language and receptively when attempting to grasp and understand the language… as practiced by natives.”

4. What is transfer? How many types can it have?
Transfer” is the central idea in the CAH. It can have positive or negative form depending on the similarities or differences of two languages. If there is a similarity between NL and TL and the old habits facilitates the formation of new habits, ‘positive transfer’ happens. When there is a difference between the two languages and the old habit makes it difficult to form the new habit; ‘negative transfer’ is taking place.

5. What is positive transfer? Give examples?
If there is a similarity between NL and TL and the old habits facilitates the formation of new habits, ‘positive transfer’ happens.
EXAMPLE:
Positive transfer such as pronunciation of English phonemes for Iranian students except for ….. and …..

6. When does negative transfer happen? Give examples?
When there is a difference between the two languages and the old habit makes it difficult to form the new habit; ‘negative transfer’ is taking place.
EXAMPLE : Negative transfer such as noun and adjective structure of English for Iranian students

7. What is the Strong Version of CA?
Those who believe in strong version of CA, consider transfer as the principal barrier in second language learning. They believe that if we are about to plan a book on language teaching, we should know the structures that will cause difficulty and those that will not; by comparing all parts of the language and culture of NL and TL.
8. What are the most important factors of the Strong Version of CA?
This attitude have some important factors:
1. They see transfer as the most important cause, and maybe the only cause, of difficulties in language learning.
2. When there is a difference, there will be a difficulty.
3. The greater the difference, the greater the difficulties will be.
4. We should compare two languages to be able to predict the probable errors.
5. After comparing two languages we can subtract the similarities, and whatever is left can be considered as the points that should be thought.
They strongly insist on the idea that the point of difficulties can be predicted.

9. Why the Strong Version of CA is not practical?
Strong version of CA beilives we should study all the parts of lanruages so is not practical . In some cases it is ambiguous.

10. What is the Weak Version of CA?
As you can see, the strong version cannot actually be practiced by linguists. So later a less ambiguous, more practicable version was introduced in which the linguist uses the best knowledge available to him to find difficulties in second language teaching.
In this version after the errors were committed by the students, the linguist will consider them as the point of difficulties.

11. What is the similarity of Weak and Strong versions of CA?
The similarities of strong and weak versions:
Both of these point of views accept the ‘interference’ as a factor in causing difficulties.

12. What are the differences between Weak and Strong version?
The differences between strong and weak versions:
1. The strong version says that all the parts of both languages and cultures should be compared (impossible), but in the weak version just the parts causing difficulties would be studied.
2. The strong version sees errors as sins, their occurrences should be prevented. The weak version accept the errors’ occurrences as a usual event in the way of language learning. In this version the errors are studied after have been committed.
3. The strong version has a predictive nature but the weak version has diagnostic and explanatory nature.

13. What is the CA procedures? Name the steps and explain each of them.
CA procedures:
In CA studies usually four steps are followed:
Selection: In this step the contrastivist chooses a certain item of the two languages to study.
Description: The contrastivist uses formal grammar to describe the two languages clearly.
Contrast: this step is the mapping/discovering of the relationship of one system to the other one.
Prediction: considering what they have found in the first tree steps, they predict the difficulties that might occur.
Verification: The analyst tries to find out whether his predictions about language learning difficulties are true or not

14. What is the level 0 of difficulty on the basis of Prator’s hierarchy?
Level 0- transfer
In this level there is no difficulty because the sounds, lexical items, or the structures of the two languages are similar, so the student just need to transfer (positively) what he already knew into the other language.
Such as most of the vowels and consonants of English and Persian:
15. /b, f, s, p,……../
Some words: door, mother, father
Some structures: garden flower گل باغچه
Flower garden

16. Name the levels of difficulty according to Prator’s hierarchy and explain one of them. Give example.
Level 0- transfer
Such as most of the vowels and consonants of English and Persian:
/b, f, s, p,……../
Some words: door, mother, father
Some structures: garden flower گل باغچه
Flower garden

Level 1-coalescence
Such as the words: teacher
Student
Cousin
Level2- underdifferentiation
Such as Persian phonemes: /x/ and /q/
مگر و چندمین

Level3-Reinterpretation
For example Persian students of English already know the phoneme
clear/l/ but they should learn a new allophone (dark /l/)
level4- Overdifferentiation
For example English structure of “to be about to”, present perfect
continuous, future in the past, past perfect continuous, etc.

Level5-Split
Such as; he, she
Table, desk
Simple present tense and present continuous tense