Clauses of Purpose
1. So as & in order to
So as
So as not
In order to
Whenever I come home late I try to be very quiet so as my father doesn’t wake up
I came in quietly yesterday so as not to wake my father
In order to prevent my father from waking up, I came in quietly
I came in quietly in order to prevent my father from waking up
He went to Paris in order to close a deal
He went to Amsterdam to close a deal
2. So that + will/would be able to or can/could
If we omit that, we lose the idea of purpose.
3. In case & lest
In case
Lest
In case + subject + verb
In case + present = “because this may happen”
In case + past = “because this might happen”