Why does Giles help Proctor in the forest?

Putnam attempts to stop Proctor from hauling his lumber claiming the land really belongs to him, that it was willed to him by his grandfather. Giles stood up for Proctor noting that Putnam's grandfather tried the same thing with his own land. 

Putnam: A moment, Mr. Proctor. What lumber is that you’re draggin’, if I may ask you?
Proctor: My lumber. From out my forest by the riverside.
Putnam: Why, we are surely gone wild this year. What anarchy is this? That tract is in my bounds, it’s in my bounds, Mr. Proctor.
Proctor: In your bounds! indicating Rebecca: I bought that tract from Goody Nurse’s husband five months ago.
Putnam: He had no right to sell it. It stands clear in my grand-father’s will that all the land between the river and -
Proctor: Your grandfather had a habit of willing land that never belonged to him, if I may say it plain.
Giles: That’s God’s truth; he nearly willed away my north pasture but he knew I’d break his fingers before he’d set his name to it. Let’s get your lumber home, John. I feel a sudden will to work coming on.