The difference between open and close here is that closed (in this sense) is not an adjective. It can be used as an adjective, but it's not a proper adjective; it's a participle (a verb used as an adjective). Participles are made from the past tense of the verb. Open is a proper adjective though, so it doesn't fall under that process of turning verbs into adjectives. It might be helpful to think of the verb open and the adjective open as different words. With close it's just a single word, a verb that can be modified with an -ed to turn it into an adjective. Open doesn't need to be modified to become an adjective; it already is an adjective. Also "the door is opened" does work sometimes. For example, "we will enter when the door is opened" or "the door is opened when we press the button" Opened is correct when you're using it as a verb/participle to describe an action/change. Open is correct when you're using it as an adjective to describe the static state of the door without implying any change. If you describe the door as "opened" you're saying it was just closed and now it's open, if you describe it as open, it may have always been open or not, there's no implication either way. It works the same way with free/freed.

Hi Lyon'ka, When we say "The door is closed", we are using "closed" as an adjective to describe the state of the door being shut. Another point to note is the fact that "closed" is an example of a participial adjective (verbs that end with -ed, -ing or -en but functions as an adjective). This is also the reason why we can say "The door is opened" to describe the position of the door that permits one to enter a room. We are not using "opened" and "closed" as verbs here. Other examples of participial adjectives include: interestING, interestED (The lecture was very interestING (adj) and we were all very interestED (adj).) On a separate note, "The door is opened." and "The door is closed." are both in the passive voice. As such, someone has opened or closed the door previously. The identity of that person is unknown here but the meaning is still complete. When we say "The door is close", we are also using an adjective, albeit with a different meaning. It means something in close proximity -- you are near the door. Lastly, "The door is open" sounds odd. I would change it to "The open door", which means that the door is in a position (ajar) that permits access into a room. "The door is opened." --Someone opened it, now it is ajar. "The open door" -- The door is ajar. The focus is not on who opened it. Hope this helps. Cheers, Lance