Just as a source needs an encoder to translate her purposes into a message, so the receiver needs a decoder to re translate. If you take a look at our discussion of the receiver, you’ll see that we considered how, for example, a blind person would not have the equipment to receive whatever non-verbal messages you send in the visual channel.
The notion of a decoder reminds us that it is quite possible for a person to have all the equipment required to receive the messages you send (all five senses, any necessary technology and so on) and yet be unable to decode your messages.
An obvious example would be:
You can see it. You probably guess that it’s a language, maybe even that it’s Arabic. You probably don’t understand it, though. In fact, it is Arabic and it does mean (but nothing very interesting). You cannot decode my message, encoded to you in that short sentence, by you. You have the appropriate receiving equipment, but no decoder. You don’t understand the code.