Yes, it is. definetely.^^/ The subject particles 이/가 make a noun into a subject in a sentence. A noun can be a subject, topic, object and predicate with proper particles or copula (like 이/가, 은/는, 을/를, 이다.) These particles and copula verb(=이다,예요, 이에요 like BE-verb in English) indicate that how nouns function in a sentence, so they ARE necessary. Supposed you've got A noun, 사과(an apple) 1) it can be a subject with the subject particles, 이/가 (some call them identifier particles^^) 사과+가 맛있다 = THE apple is delicious(specific apple, your own opinion....or.....it wasn't anything else but apple) 2) as a topic with the topic particles, 은/는 사과+는 맛있다 = AN apple is delicious.(general statement) 3) as an object with the object particles, 을/를 사과+를 먹었다 = I ate an apple. 4) as a predicate with coplua verb, 이다(이에요,예요) 그것은 사과+이다 = It is an apple. (그것은 사과+예요, in spoken) \^o^/

In the Korean language, the grammatical relations between the sentence components are defined by the suffixes (ending particles). I take an example of “Tom likes a cat”. If I change the word order, the sentence will have a totally opposite meaning or even it is impossible to understand. A cat likes Tom. (The meaning becomes opposite.) Likes a cat Tom or Likes Tom a cat. (It is hard to figure out what these words mean to say.) In Korean, “고양이” means a cat and “좋아한다” means “like”. Tom is 톰. The most grammatical way to say the example in Korean is “톰은 고양이를 좋아한다”. However, we can also say “고양이를 톰은 좋아한다”. As an extreme instance, even though we say “좋아한다 톰은 고양이를” or “좋아한다 고양이를 톰은” in whichever ways we can, we don’t have any difficulties to understand the speaker. It is because of a case suffix. In the Korean example, two case suffixes are used, “는” and “를”. “는” and “를” assign subjective and objective case to nominal phrases each. Therefore, no matter where a word is placed in a sentence, we can identify its grammatical role. In Korean, there are not only case suffixes but also numerous suffixes which determine syntax. Therefore, it is very important to know all the different kinds and roles of the suffixes in learning Korean. Finally, I will mention one more example of the suffixes, an attributive suffix for your better understanding. The Korean language has no relative clauses. Instead, verbs inflect to modify a noun. I know a man who walks very fast. In the above sentence, the relative clause “who walks very fast” describes the noun, a man. In Korean, however, the verb “걷다” which is “walk” in English inflects to form an adjectival clause. That is to say, “걷다” is inflected to “걷는” and “는” here is an attributive suffix. So, the translation of the English example into Korean will be “나는 매우 빨리 걷는 사람을 알고 있다.” When I rewrite the English sentence according to the Korean word order, it structure will be as follows. (The words in brackets are the Korean suffixes or an ending particle.) “I(는) fast walk(는) man(을) know.” * the first “는”: a subjective particle * the second “는”: an attributive ending particle * the last “을”: a objective particle