は and が

Introduction

Most Japanese learners know the difficulty of differentiating between the particles は and が, but I feel that there aren't a lot of well-informed and well-written articles on the subject that are written in English. Sure, there are some that explain the simple basics in good detail, but many common errors are a result of the lesser talked about. Not only do I plan to explain the reasons for common errors of は and が, but other particles will be brought up, such as にとって. Before this lesson begins, I need to say this: I hate the overdone "私は means 'as for me'" description. It may help beginners think of this way in simple sentence constructions such as 私はピザが好き, but I feel as though this misdescription of は will hinder your understanding for intermediate and advanced sentence constructions. I advise everyone to forget this "as for ___" way of thinking.

First, let's begin with the foundations of は and が. Typically, は is used to information that is well-known for both the speaker and listener; が is used for presenting new information. Take this example sentence using both particles:
さくらはきれいだ。 さくらがきれいだ。

In both sentences, さくら is the subject. In the first example, the statement suggests that everyone knows that cherry blossoms are beautiful. One would never even have had to see them in their lifetime to know that. Using が suggests a condition in which one would have to see cherry blossoms firsthand before coming to the conclusion that cherry blossoms are beautiful. These two example sentences show that は and が can both be used but have slightly different meanings for the Aは/がB construction. This differentiation is usually what is discussed on は vs. が lessons.

Since there are no articles in Japanese (a, an, the), some Japanese learners may think of は and が like this (yes, there are ways to to express this in Japanese, but it is very proper and not often seen, except for academic and scientific writing styles):
女がいました=a girl
女はいました=the girl

The sentence with が would be "a girl" because it presents new information, whereas は does not. Here is a short bonus lesson on passive verbs. When a fact is presented without a subject, the passive form is used (subject that performs the verb). 答えは書かれていません=there is no answer written. If we had a subject (someone who would write the answer), we could write 田中さんが書いた=Tanaka-san wrote it. The above-mentioned proper usage of は and が is very basic but will get much harder from here. This is typically all that is covered in most written lessons online. However, this article is not meant for beginners but rather Japanese learners intermediate and above for whom have a simple grasp of は and が or still have trouble with these particles.

Let's start with simple mistakes that aren't actually grammatically correct but what are considered normal and natural Japanese. When people go to a store or restaurant, they may ask if the place has what they want. Which is correct?

Mサイズはありますか?
Mサイズがありますか?

You may be surprised. Actually, using no particle is correct.
Mサイズ、ありますか?is the most natural way to say it. Using a particle for a question like this is not completely unheard of. The simplest explanation for why to omit the particle is that the listener can read your mind for which particle to use, and therefore is not necessary. Particles are often omitted even in standard Japanese, and using them may sound strange, but don't worry about it.

The Subordinate Clause

Next, let's look at は and が misuse in more advanced sentences. We'll first look at misuse for 従属節内, which means errors within the subordinate clause. For those unfamiliar with the term, a subordinate clause is a part of a sentence that cannot be a sentence by itself. Here are two simple examples in Japanese.

❌ 私あつ森をしているとき、友達が来た。
❌ 友達できないために、日本語の会話は練習できない。
❌ 彼女その事故の知らせを聞いたとき、泣いた。

In both of these sentences, は should be が. The reasoning is that in subordinate clauses, the subject fundamentally takes が as its particle. Like 従属節内 (subordinate clauses), 名詞節内 (noun clauses) and 名詞修飾節 (noun modifiers), follow similar rules. Combining two simple sentences may make it easier to understand the reason for using が over は when using noun modifiers:

これはぬいぐるみです。
僕は東京で買った
これは僕東京で買ったぬいぐるみです。

が is switched from は because 東京で買った is modifying ぬいぐるみ and the speaker wants to let the listener know that the speaker bought the plush from Tokyo. Also, notice how が is used instead of の. Using の changes the meaning. Let's compare.

これは僕が東京で買ったぬいぐるみです=I bought in Tokyo. It is clear that 僕 did the action of buying.
これは僕の東京で買ったぬいぐるみです=who bought the plushie? It is unclear who bought the plushie, but it is clear who owns the plushie. The sentence roughly means "This is my plushie that was bought (by someone else) in Tokyo."

Common Mistakes in Using は vs. Other Particles

Next, we'll look at mistakes in は in place of other particles.

❌ 来週の月曜日新しいアニメが始まる。
☑ 来週の月曜日新しいアニメが始まる。

While the speaker may think that the topic is about next monday (which it could be), the phrase "next monday" designates the time in this specific example, so it's correct to use に and not は. Oftentimes は is not used for time words, but that is not always the case. I think because 今日は is used in a lot of beginner textbooks, beginners think that は always comes after works like 今、今日、来週. We could change the sentence slightly to make use of は instead of に.

☑ 来週の月曜日は、僕が新しいアニメを見始める。

If we compare the two sentences, "next Monday" is used as a designation for when the anime starts, whereas the sentence using は just tells the listener that on Monday, "I will begin watching the anime." It could be any other day but the speaker will choose to watch on Monday. In the other example, the anime starts on Monday and there is no other choice. "Next Monday" serves as two difference purposes.

❌ トムさん合格するのは大切です。
☑ トムさんにとって合格するのは大切です。

These two examples show the reason why I particularly hate the "As for ___" meaning of は. See if you can identify the problem with the direct translations of these two examples:

As for Tom, passing the exam is crucial.
For Tom, passing the exam is crucial.

にとって can mean "for, to, as for as someone is concerned." The "as for ___," in my opinion, makes understanding other particles like にとって (and other with the meaning of "for") difficult to understand, which is my personal reasoning for advising against thinking of は as "as for ___." I should add that because beginners and even lower intermediate students may not have many particles in their repertoire, then it is understandable that は may be overused for particles other than が. Next, let's take a look at mistakes with が and introduce uses of は that I intentionally left out.

Common Mistakes Using が

First, it is a general rule that question words such as どこ、どう、何、だれ all use は instead of が for the subject.

❌ スミスさんどこですか?

❌ 中村 :スミスさんは日本語どうですか?
❌ スミス:日本語難しいです。

は is the correct particle for each of these examples.

☑ スミスさんどこですか?

☑ 中村 :スミスさんは日本語どうですか?
☑ スミス:日本語難しいです。

Next, we'll learn about how は can be used for comparisons. Typically, we learn sentences like these to talk about things we like and dislike:

ピザ好きです。野菜嫌いです。

However, if we want to combine these two sentences (which shows comparison), we use は instead of が.

ピザ好きですが、野菜嫌いです=I like pizza but hate vegetables.

Comparisons don't just have to be about opposites such as "like/not like," like in this example:

Nintendo Switch好きですが、PS4ありません=I like the Nintendo Switch but don't have a PS4.

Another common mistake is the use of 皆が in place of みんなで.

努力した。
みんな努力した。

When using counter words, those typically do not use a particle.

❌ 一つあります。
☑ 一つあります。

Main Points

First, don't get discouraged if you make a mistake with は or が. It's simply natural. Also, don't worry about whether to use は or が when only using basic, short sentence structures. Not only is it silly to debate which particle to use when using such basic sentences, but it is also a waste of time if you want to properly master both particles. Having more familiarity with the language: speaking, reading, or writing longer paragraphs will help immensely in mastering は and が. I saved this last point to help save much confusion. If you're using a simple sentence and it has a neutral meaning (not positive or negative, nor comparing with or against anything), then both は and が are correct to use, and it is really no big deal. I hope this short guide helped with a few of the most important common mistakes. Of course, this guide did not go over every possible mistake that one could do, but I hoped that it helped.