It is used to combine or rewrite sentences for denoting a purpose.
To understand it, let’s look at the following sentences,
Mathew saves Rs.5000 every month from his salary. He wants to buy a Laptop.
Of these two sentences, whereas the first one shows an action ( saving Rs.5000 ), the second denotes a purpose ( buying a Laptop) by the action mentioned in the first sentence.
The above sentences can be combined or rewritten with so that maintaining the same idea as follows,
Mathew saves Rs.5000 every month from his salary so that he can buy a Laptop.
For combining or rewriting the sentences, it can be understood from the above answer is that, the sentence denoting the action is to be written at first and then to be followed by so that. After that the sentence denoting the purpose is to be written later.
But while writing the second sentence, the ‘to infinitive’ ( here, to buy ) of the sentence must be changed into ‘finite verb’ ( verb having a tense form) by giving it the helping verbs ‘will/shall/can/may’ and ‘would/should/could/might’ just after writing the subject, according to the tense form of the sentence.
If the tense form of the sentence is present, then the helping verbs ‘will/shall’ ( denoting future) or ‘can’ (denoting ability) or ‘may’ (denoting possibility) is to be used to change the ‘to infinitive’ into ‘finite verb’. In the above second sentence, we can understand by the verb ‘wants’ that the sentence is in present tense. That is why, the helping verb ‘can’ is used with the verb ‘buy’.
So, in the above answer, we can see the second sentence ( showing the purpose) of the question ‘ He wants to buy a Laptop’ is rewritten, by giving the helping verb ‘can’( as the sentence is in present tense), to change the ‘to infinitive’ ( to buy) into ‘finite verb’ ( can buy), as ‘ He can buy a Laptop’
If the tense form is past, then the helping verbs ‘would/should’ ( denoting future) or ‘could’ ( denoting ability) or ‘might’ ( denoting possibility) should be written, as seen in the following answer,
Question: Jacob finished the work in time. He wanted to go home early.
Answer : Jacob finished the work in time so that he might go home early.
- Justin has applied for a job in USA. He wants to settle there.
Justin has applied for a job in USA so that he can settle there.
- Martin worked hard. He aimed to earn more money for his sister’s marriage.
Martin worked hard so that he might earn more money for his sister’s marriage.
Thus we have studied to combine or rewrite sentences with So that for showing a purpose.