Traditions: The Ring Finger...why?

The ring finger is the fourth digit of the human hand, and the second most ulnar finger, located between the middle finger and the little finger. It is also called digitus medicinalis, the third finger, digitus annularis, digitus quartus, or digitus IV in anatomy.

During the 3rd century in Greece, the ring finger was the index finger.

In India it was the thumb.

The Egyptians believed that a special vein, which they called a "vena amoris" or vein of love, ran from the third finger on the left hand, directly to the heart. By putting on a fitted ring, the affections were bound in and could never flow out the fingertips. Also, this finger although not the smallest on the hand is the weakest and most dependent on the others for help in lifting and holding. It seemed to symbolise the young wife supported by the strength of her husband.
The "ring" finger has sometimes been on the left hand, sometimes on the right, according to country and custom. Among English-speaking christians, it has been on the left since the edict of Edward VI in 1549.

For this reason, the fourth finger of the left hand has been adopted through the ages as the ideal place for the wedding ring.

Here's a beautiful and convincing explanation given by the Chinese:

The thumb represents your parents.

The second finger/index finger represents your siblings.

The middle finger represents yourself.

The fourth finger/ring finger represents your life partner.

The little finger represents your children.

First, open your palms, face to face. Bend the middle fingers and hold them together, back to back. Second, take the rest of your fingers and thumb and place them tip to tip.

Now, try and separate your thumbs which represent your parents, they will open. Your parents are not destined to live with you for the rest of your lives. They will leave you sooner or later. Join your thumbs as before.

Now take and separate your index fingers representing your siblings. They will also open. Your brothers an sister will make their own families and will lead their own separate lives. Now join your index fingers again.

Now separate you little fingers representing your children. They will open too. Your children will grow up, settle down and begin on their own family someday. Now bring your little fingers together.

Finally, try and separate your ring fingers which represent your spouse. You will be surprised to see that you cannot separate them, because husband and wife are meant to be together all their lives, through thick and thin.

Cool, right?