In Wireless Networks, you can put your wireless card in Promiscuous or in Monitor Mode.
What is the difference between these two modes ?
Capture packets on a network that you have connected to. This is likely what you need to be in if you want to analyze packets (Wireshark, tcpdump, etc.)
Capture packets regardless of connected network. No association to AP needed (and no authentication). Because it is not connected to a network, you can't process the Ethernet info.