Have I understood this correctly?
To use a key and lock analogy. With an asymmetric pair of keys (when used to encode) can either key be used to encode the message (close the lock) and only the "pair" be used to decode (open the lock)?
Taking the key analogy further, is it a useful comparison to say that the first key of the pair changes the lock after it is used so that only the "not yet used" key of the asymmetric pair can open the lock?
The description of keys as "public" and "private" is only a convention that relates to their use and not the order in which they are used i.e. can use 3.1 public then private (encoding for one intended recipient) or 3.2 private then public (digital signatures)?
Edit: Wording of point 2 altered following comment by Maarten Bodewes.