Definite article — “on television” vs. “on the radio”

Solution 1:

These are my assumptions based on the the Longman Dictionary entry for 'television'and the examples cited there. According to this entry,

The word television can refer to a) the equipment as well as b) the programmes broadcast on television.

From the examples cites there, I understand that we use the definite article when we are referring to the device.

Lucy turned on the television to watch the evening news.

On the other hand, it looks like we can omit the definite article if we are referring to the programmes.

In the evenings I like to relax and watch television.

The third entry on the dictionary is:

on (the) television:broadcast or being broadcast on television:

What's on (the) television tonight?

Probably, in this type of usage with the preposition, it is fine to omit or use the definite article.

Solution 2:

I have thought about this for a long time, but I am afraid I can think of no reason why it is as it is. This is just idiom; you need to learn it without any overarching rule, alas.

There are several ways in English to denote that you are talking about something in general rather than a specific instance:

• Man has been on the moon. Love is banal. Pottery is an important technology. (No article)
• The wheel is a great invention. The most poisonous spider in Europe is the Black Widow. (Definite article)
• A jaguar would never eat an elephant. (Indefinite article)
• Penguins hate polar bears. (No article, plural)
• The Assyrians do not take prisoners. (Definite article, plural)

In some cases you could use several ways; not all are possible in each case.