During Lincoln's youth, and particularly after the death of his mother, Abraham's relationship with his father changed and became increasingly strained. Due to his failing eyesight and likely declining health, Lincoln relied on Abraham to perform work needed to run the farm. He also sent Abraham to work for neighbors, generating money for Thomas. Michael Burlingame, in his book "The Inner World of Abraham Lincoln" classified Abe's subservience, "Abraham Lincoln was like a slave to his father," he penned in a secret biography.