That used to be true, but not so much anymore. Cox, Comcast, and Time Warner (Spectrum) have been encrypting all their cable channels for several years now, even the ones which shouldn’t be encrypted because they’re available over the air. Verizon in areas with FIOS uses their own system – you need their FIOS modem to convert the fiber optic signal back into a coax cable signal. With Charter merging with Time Warner to form Spectrum, and AT&T merging with Spectrum, that’s pretty much all the major cable companies which encrypt basic cable now.
To receive it, you need to either rent a cable box from the cable company, or you buy your own cable box and rent a CableCard (usually about $5/mo) from the cable company. The cable box or CableCard holds the decryption keys, allowing you to view the encrypted channels according to your subscription level.
If your cable TV service is through a smaller cable company (not one of the majors), your chances are better at getting unencrypted basic TV. You may also be in range to pull in over-the-air HDTV with an antenna.