“Is this the man that you spoke of?” Better, “of whom you spoke.”
“These are principles that our forefathers died for.” Rather, “for which our forefathers died.”
Prepositions are often omitted when their use is necessary to the correct grammatical construction of the sentence.
“They now live on this side the river.” Say, “on this side of the river.”
“Esther and Helen sit opposite each other.” It is more correct to say, “sit opposite to each other.”
“John is worthy our help.” Better, “of our help.”
“What use is this to us?” Of what use, etc.
“This law was passed the same year that I was born.” Say, “In the same year,” etc.
“Washington was inaugurated President April 30, 1789.” Some critics insist upon the insertion of on before a date, as “on April 30,” but general usage justifies its omission. With equal force they might urge the use of in before 1789. The entire expression of day, month, and year is elliptical.