Originally Posted by: chrisscott1011

What differentiates a chord to be major or minor?

The interval formula, specifically the 3rd.

Every major chord consists of the root, major 3rd & 5th scale degree of its parent scale.

Every minor chord consists of the root, minor 3rd & 5th scale degree of its parent scale.

All chord qualities (major, minor, dominant, etc.) are determined by certain, specific scale degrees being included.

I cover the basics of chord theory in this tutorial.

https://www.guitartricks.com/tutorial.php?input=426

Hope that helps!