Is there big difference between Chinese and its dialects (such as Cantonese)?

It is a good question from an iTalki friend.

Q:
Are there many differences between Mandarin Chinese and Cantonese? Once you learned Chinese, is it becomes easier for you to learn Cantonese?

A:
Cantonese is a kind of Chinese dialect. Basically, Mandarin Chinese and Cantonese share the same grammar and writing system (though slight differences exist); the most different part is the pronunciations. Without special learning, it is difficult for a Mandarin speaker (who didn't learn Cantonese before) to understand a Cantonese speaker's speech,

However, though the pronunciation difference between Chinese and Cantonese is so big that it's difficult for Chinese speaking people and Cantonese speaking people to mutually understand each other. Mandarin Chinese and Cantonese still share some pronunciation similarities~  Their relationship is just like uncle and nephew... They are different, but not dramatically different (like Chinese vs. European languages are)

Since Mandarin and Cantonese are relatives, when one can speak Mandarin Chinese, it's definitely easier for him to learn Cantonese (because writing system and grammars are almost the same), and vice versa.