The straight sword is an extension of the hand.
In the study of Taiji we need to learn the principles particularly that of the 3-Count and 5-Count properly. Otherwise, when we learn the straight sword we will have a hard time catching the proper timing required to move the straight sword in tandem with the body.
When I see my student play the straight sword form I see this problem so it bears repeating the importance of correct learning. In the initial stages of wielding the straight sword the student would normally not feel anything is off and wrong.
But when he has worked on it for some months he will start to have doubts on certain movements and the changes. If he has learned the 3-Count and 5-Count properly in the long form then he will make the connection between the empty hand and the straight sword as an extension of it. Subsequently, he will be able to apply the lessons previously to solving the problems of the straight sword.
Otherwise, he will have a hard time figuring things out especially when some of the changes in the movements of the straight sword can be very subtle and without the means to control the timing the movement would look off and the power will not come. Sometimes, one can cheat by doing the movements quickly to cover up but at the end of the day wrong is wrong and one will still not be able to control the straight sword.