Need Help With a Rick Beato Lesson

[Jak Angelescu]

Hey theory gurus! Can you help me figure out how exactly he knew the Eb7 chord was the dominant chord to find the key signature? I tried rewinding it over and over again and I can’t make sense of how he knew that. He states he knew that it was the five chord because it’s the V chord in only one key signature but I want to know how he knew that was the five chord. Thank you all so much!
Time stamp is 7:31

 

[idssdi]

How I understand it is that in each key there’s only one mode or chord that has the characteristic of a dominant chord which is the V chord or mixolydian.

 

[Syn Gates]

You’re 100% correct Jak! You look for a dominant chord preceding a major/minor chord a 4th away(the I chord is a 4th below the V). So simply put, you are looking for V I cadences(progressions) called “Authentic Cadences”. Great work figuring it out and I LOVE that you’re checking my friend Rick out, he truly is the master!

 

[Jen Hapke]

I remember watching the video the frist time and my brain just exploded after about 3 minutes and until now I never got through the whole video. I guess I will give it another try someday

 

[Jak Angelescu]

Thanks Syn!!! You helped a lot!