Watch the Week 1: Matching Elements online guitar lesson by David Wallimann from Playing Modal Made Easy

Any musical elements can be classified into the following two main categories: Major or minor.

The 3rd determines where the element goes.

Major ModesMinor modes
IonianDorian
LydianPhrygian
MixolydianAeolian

Locrian


Remember that in order to play in key, musical elements need to match. For example, if a chord has a major 3rd, you will need to use a major mode. The more notes a chord has, the less options you will have as far as which mode to use.