OK. It looks like some people felt offended and flagged my post. Lets calm down.
First, I invite everyone to think a little bit about how we should pray and how our very posture and actions are representations of our inner states. Think about how logic this thought is: If I am speaking to a Saint or God Himself, why would I do it in a disrespectful way?
When someone speaks to a judge, they stand. When our boss or some company director joins a meeting, everybody stands in sign of respect. When a king/queen walks by you, you bow to him/her. And when speaking to a king/queen, we kneel. By the way, we should bow to priests when they approach and kneel to bishops when they do the same. These are all signs of RESPECT. Body language is more important than most people realize.
Second, regarding exceptions, of course they exist. OBVIOUSLY, people who can’t stand or kneel or prostrate are not obliged to pray in any of these ways. Another example is when a person is commuting or traveling and have to stay sit. Explaining obvious exceptions such as these shouldn’t be necessary…
Third, back to the positions. The rule is: if you can, DO THE RIGHT THING. Pray with all your mind and all your heart and the most decent posture (depending on the type of prayer), which are standing, kneeling or prostrating.
The Mass teaches us how to do the right thing. The priest is ALWAYS standing (except between the colect and the Gospel in High Mass, when he ends the prayer at the altar and then sits to wait the choir finish the chant). And we, the laity, while atrending Mass, only sit during the Epistle and some other minor parts. These are the exceptions. The rule during Mass is: stand during the prayers or kneel (this second especially when Our Lord is truly present on the altar).
Finally, I ask once more. Think about it. Don’t reply right away. Actually, don’t act right away if you get angry. I know most people here are reasonable.