What does this mean?
"When you use the impersonal construction il est + adjective + de, keep in mind that il must be a dummy subject. If it's a real subject, you must use à instead of de."
- Can someone please explain this, what's a dummy subject??
Dummy subjects are just the type of subject used in the construction of statements that don't initially start with a real subject (think something that doesn't have matter nor is an idea). In English, we use "it" as our dummy subject, and "il" in French. Usually dummy subjects can be avoided if you change the construction around a bit and use the verb as the noun, similarly to how you can change the construction in English.
It is hard to make good grades/Making good grades is hard = Il est difficile de faire de bonnes notes/Faire de bonnes notes est difficile
As you can see in the above sentences, there is no dummy subject in the second translations because they both follow the same construction of (Gerund-->is/est-->Adjective).
Also, as far as I know, dummy subjects are never used in French when describing an actual activity/idea/thing. Instead, using the pronoun "ce" is more appropriate. Among the four below sentences, only the first is correct.
C'est facile à faire. Il est facile de faire. Il est facile à faire. C'est facile de faire.
Also, take note that in spoken French, many speakers have the tendency to use "ce" as the dummy subject, although this is technically incorrect.
Hope this helps :)
I didn't have a clue and I've been using dummy subjects without knowing what they are. I have been deceived all my life.
"When we use the words it and there to begin a sentence without a referent (a noun the pronoun is referring to), we’re using a dummy subject." https://www.dailywritingtips.com/the-dummy-subject/
Dummy subjects are constructions who lack a subject (this sentence has a real subject "Dummy subjects")
But it is apparent that there are other kind of sentences (this is a dummy subject since it doesn't have a real subject, the subject is "it's")
"English clauses which are not imperatives must have a subject. Sometimes we need to use a ‘dummy’ or ‘empty’ or ‘artificial’ subject when there is no subject attached to the verb, and where the real subject is somewhere else in the clause. It and there are the two dummy subjects used in English" https://dictionary.cambridge.org/grammar/british-grammar/about-words-clauses-and-sentences/dummy-subjects
Ex: It's there. There's many ways to do it.
In French the constructions "Il est + adjective" are dummy subjects.
Il est bon de savoir (Dummy subject "Il est-It is") Il est difficile de comprendre (Dummy subject "Il est-It is")
"C'est + adjective" is a real subject for impersonal expressions.
C'est bon à savoir (Real subject, impersonal "C'est-that is") Les sciences sont difficiles à comprendre. (Real subject "Les sciences")