Chacun son gout: what's observable and what's not?

In an exercise we did in my Program Program Planning & Evaluation for Adult Education (whoa that's a mouthful when you type it out!) class, I had the opportunity to reflect on verbs that I've taken for granted when it comes to defining learning outcomes in past courses, where i've written them or have been subject to them by others. I realized that some verbs are not as clear and "observable" as I had once thought or overlooked.

Let's consider the following:

• Understand
• Demonstrate
• Express
• Describe
• Advocate 

How can these be measured? How can these be specifically observed to determine if they have been acheived by the participant?  For some, verbs like "to demonstrate" mean to physically show something is understood, but perhaps "to understand" cannot be physically demonstrated.  Some verbs lead to describing or prescribing future actions and do not appropriately or necessarily address the short-term outcomes desired by a program.
I'm certainly more aware of this now as I begin to craft learning outcomes and program objectives.