In a grammar class I'm enrolled in, one of the diagnostic tests contained the following question:
"Blocking" is when a television network schedules a less popular program between two popular ones
According to the test, a good revision would be:
"'Blocking' is a television network's practice of scheduling a less popular program between two popular ones."
Why is it grammatically incorrect to connect two subjects with "is when" or "is how", as in the above example? My teacher called it an 'illogical expression.'
Are there any other "is __" phrases that I should avoid?