A very basic breakdown:

Instrumental

• We join with others to take collective action in order to achieve measurable goals. Our actions are tactics within strategies, which we hope will result in tangible successes/gains/improvements to people’s lives.
• We are concerned with results. We evaluate whether our actions are moving us toward making substantial change.

Expressive!

• We also join with others to take collective action because it makes us feel good. Our actions express our values, our identities, and our sense of belonging in the group or the movement.
• Expressive aspects of collective action and movement participation are important — this is what feeds us, makes us feel like we’re not alone, and keeps us going.
• WARNING: you can fulfill your expressive motivations without ever winning anything!

A longer elaboration of this dualism, authored by Joshua Kahn-Russell, Zack Malitz, and yours truly, is available at BeautifulTrouble.org.