Changes

Even if the adjective or verb following the topic is modified, "ga" is still used, as the relationship between the topic and the adjective is still one to one. Thus the sentences "<font color=red>Nigatsu ni yuki</font> '''ga''' <font color=blue>furimasu</font> (In February snow falls) and <font color=red>Nigatsu ni yuki</font> '''ga''' <font color=blue>yoku furimasu</font> (In February, snow often falls), the link is between "snow" and "falls.”

Even if the adjective or verb following the topic is modified, "ga" is still used, as the relationship between the topic and the adjective is still one to one. Thus the sentences "<font color=red>Nigatsu ni yuki</font> '''ga''' <font color=blue>furimasu</font> (In February snow falls) and <font color=red>Nigatsu ni yuki</font> '''ga''' <font color=blue>yoku furimasu</font> (In February, snow often falls), the link is between "snow" and "falls.”

Another important difference between "wa" and "ga" lies in the topic of the sentence itself. An unknown pronoun (who) can ''never'' take the "wa" particle - you cannot say, for example, "Dare '''wa''' hon '''o''' yomimasu '''ka'''," for "Who will read a book?" Using "wa" in this case, almost translates as "As for who will be reading the book?" and makes no sense. Here you would say "Dare '''ga''' hon '''o''' yomimasu '''ka'''." Simply put, "who" can be the subject of a sentence, but not the topic of a sentence, and hence is marked with "ga" and not "wa".

Another important difference between "wa" and "ga" lies in the topic of the sentence itself. An unknown pronoun (who) can ''never'' take the "wa" particle - you cannot say, for example, "Dare '''wa''' hon '''o''' yomimasu '''ka'''," for "Who will read a book?" Using "wa" in this case, almost translates as "As for who, he will be reading the book?" and makes no sense. Here you would say "Dare '''ga''' hon '''o''' yomimasu '''ka'''." Simply put, "who" can be the subject of a sentence, but not the topic of a sentence, and hence is marked with "ga" and not "wa".

"Ga" is also used for emphasis, where there is a need to distinguish a person or thing from all the others. It is a difficult concept to explain, as in English, this difference is often conveyed in the tone of voice being used.  

"Ga" is also used for emphasis, where there is a need to distinguish a person or thing from all the others. It is a difficult concept to explain, as in English, this difference is often conveyed in the tone of voice being used.