I would like to know the difference in the meaning between "1" and "2".
1. I was so tired (that) I couldn't help yawning.
2. I was so tired, (that) I couldn't help yawning.
net 1. I was so tired (that) I couldn't help yawning. Being tired was the cause of the yawning.
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smartenglish@hanmail.net1. I was so tired (that) I couldn't help yawning.
Being tired was the cause of the yawning.
smartenglish@hanmail.net2. I was so tired, (that) I couldn't help yawning.
If you don't include 'that', you have a mistake called a comma splice.
You can correct that as follows.
I was