Adding lateral support for the gate post, also helps to ensure that the top will not bend towards the gate, as shown in Figure 4.
Figure 4 - Lateral support for gate post
Adding a top (making an arbor) and bottom cross piece, from the hinge gate post to the latch gate post will keep both posts at an equal distance, as shown in Figure 5, and ensure that they do not shift.
Figure 5 - Building an arbor across gate posts
Figures 3, 4, and 5 shown how to support the hinge side fence post when the gate is in the closed position. The stresses sustained when the gate is in the open position should also be considered prior to construction of the gate posts.
To ensure that the posts remain plumb and square when the gate is opened, it is necessary to add structural support in that direction. The simplest method is to place another post in line with the hinge post and in the direction of swing of the wood gate, as shown in Figure 7. The perfect situation would be to have the gate post and the structural about 2 feet apart, but even a distance of 1 foot will make a substantial difference tot he structural integrity of the gate post.