What claim language should be avoided in Korea?

Chanjoong Kim, Partner · Published 12 November 2026

Last verified 9 October 2026

Types of unclear expressions at a glance

As of October 2026. The examples in the table are those given in the Examination Guidelines, Part 2, Chapter 4, 4. [3]

The basis is Art. 42(4), subparagraph 2 of the Patent Act, and the Act has no list of prohibited words

The Patent Act does not prohibit specific words. What Art. 42(4), subparagraph 2 requires of a claim is that the invention is stated clearly and concisely. [1]

Supreme Court Decision 2014Hu1563 Decided April 7, 2017 held that only clear statements are allowed in a claim. It held that terms that express the configuration of the invention unclearly are not allowed in principle. [4] The Supreme Court of Korea gave Art. 97 of the Patent Act as the reason. The scope of protection of a patented invention is determined by the matters stated in the claims. [1][4]

The assessment is not made word by word. The same decision held that whether the invention is stated clearly must be assessed case by case. The test is whether a person skilled in the art can clearly understand, from the statements of the claims, the invention for which a patent is sought. The description of the invention, the drawings and the common general technical knowledge at the time of filing are taken into account. The decision also held that the assessment must not be made uniformly on the basis of the terms used in the claims alone. [4]

The Examination Guidelines follow the same test. An unclear part can be a minor defect in the statement. If a person skilled in the art would not understand the invention to be unclear because of that defect, the claim is not treated as unclear. The same applies where the invention can be clearly understood from the description of the invention, the drawings and the common general technical knowledge at the time of filing. [3]

An application that does not meet Art. 42(4), subparagraph 2 has a ground for rejection (Patent Act, Art. 62, subparagraph 4). [1] Before a decision of rejection (decision to reject a patent application), the examiner must notify the grounds for rejection and give an opportunity to file a written argument (Art. 63(1)). [1] After registration, non-compliance with Art. 42(4) is a ground for invalidation, and a trial for invalidation can be requested for each claim (Art. 133(1), subparagraph 1). [1] For patent rights for which the registration of the grant of a patent (registration of establishment of a patent right) was made before 1 March 2017, the former Art. 133(1) applies (Addenda to Act No. 14035, Art. 21). [1] The same subparagraph of the Patent Act in force from 1 July 2014 also lists non-compliance with Art. 42(4) as a ground for invalidation. [5]

The current wording of Art. 42(4) applies to applications filed on or after 1 January 2015. Examination and trials of applications filed before that date follow the former provisions (Addenda to Act No. 12753, Art. 8). [1] The former Art. 42(4), subparagraph 2 read “발명이 명확하고 간결하게 기재될 것” (the invention is to be stated clearly and concisely). [5]

Expressions of optional matter, degree, negation and numerical limits are listed as examples

The Examination Guidelines give four groups of examples of expressions that make the configuration of the invention unclear (Part 2, Chapter 4, 4.(3)⑤). [3]

• Matter added optionally or alternative matter, stated with words such as “if desired” (소망에 따라), “if necessary” (필요에 따라), “in particular” (특히), “for example” (예를 들어) and “and/or” (및/또는)
• Expressions with an unclear basis or degree of comparison, such as “mainly” (주로), “as a main component” (주성분으로), “as a main process” (주 공정으로), “suitable” (적합한), “an appropriate amount of” (적량의), “many” (많은), “high” (높은), “most of” (대부분의), “almost” (거의), “approximately” (대략) and “about” (약)
• Negative expressions such as “except for …” (…을 제외하고) and “not …” (…이 아닌) that make the claim unclear
• In a numerical limitation invention, a numerical limitation with no upper or lower limit, a numerical limitation that includes 0, and a dual numerical limitation in one claim

The same proviso is attached to all four groups. It has two requirements. The meaning of the expression must be clearly supported by the description of the invention, and there must be no problem in specifying the invention. In that case, the claim is not treated as unclear even though the expression is used. [3]

“A and/or B” is read as stating both “A and B” and “A or B”. The examiner assesses the support requirement (Art. 42(4), subparagraph 1) and the clarity requirement (subparagraph 2 of the same paragraph) for each of the two cases. The examiner also considers whether one claim claims several inventions of different kinds. [3]

A numerical limitation that includes 0 has an exclusion. If the component that can be 0 is not an essential component but an optional component, it is excluded from the examples. In the Examination Guidelines, an optional component is a component for which the specification clearly states that it does not have to be included. [3]

Stating a broad range and a narrow range together in one claim with “preferably” (바람직하게는) is an expression that the Supreme Court dealt with directly. The claim in Supreme Court Decision 2014Hu1563 contained the statement “a group having 1 to 20 carbon atoms, preferably a branched or unbranched alkyl or alkoxy group”. [4] The Supreme Court found that it was not necessarily clear whether the statement meant the whole of the broad range before “preferably” or the narrow range after it. It held that a statement that can be interpreted in several ways depending on the point of view does not meet the clarity and conciseness requirement. [4] In that case, the description of the invention contained only the same content as the claim, so the meaning did not become clear even when the description of the invention was taken into account. [4] The decision also quoted the original claims as filed in the international patent application of 8 June 2006. In that original text, the word corresponding to “preferably” is “vorzugsweise”. [4] The former Patent Act, Art. 42(4), subparagraph 2, as it stood before the amendment of 3 January 2007, applied to that case. The Supreme Court stated that the former Act, although worded differently, had the same purport. [4]

The same content is treated differently when it is stated in an alternative form. The Examination Guidelines allow a generic concept and a specific concept to be stated as alternatives in one claim. The condition is that the two share a common property or function. The example in the Examination Guidelines is “a method wherein X is performed at 120-200℃ or 150-180℃” (Part 2, Chapter 4, 4.(6)). [3]

A referring word and a term must each point to one thing

If the referent is unclear and the configuration of the invention is therefore unclear, Art. 42(4), subparagraph 2 is not met. The example in the Examination Guidelines is a claim that recites several kinds of gear. If the claim refers to a specific gear only as “the gear” (상기 기어) and not as “the spur gear” (상기 평기어), it is not possible to know which gear is meant. [3]

The same applies where technical terms with the same wording perform different functions. Unless the function of each is limited in the claim, or the terms are distinguished by reference signs of the drawings, the claim falls under an unclear type (Part 2, Chapter 4, 4.(3)⑦). [3]

However, an obvious error is not treated as non-compliance. The Examination Guidelines give three types (Part 2, Chapter 4, 4.(4)). [3]

• The claim says “the ○○○” (상기 ○○○) although “○○○” does not appear earlier in that claim or in the claims it refers to, but the invention is clearly understood when the claim is read without “the” (상기) in the light of the description of the invention and the drawings
• The referring wording and the wording of the referent are not completely identical, but they correspond in meaning and the referent can be clearly identified
• In a claim that refers to two or more claims, some of the claims referred to have been deleted, but the invention is clearly understood when the claim is read without the deleted claims

The Examination Guidelines provide that a decision of rejection must not be issued on the basis of these three types. If there is no other ground for rejection, the examiner makes an ex officio amendment when issuing the decision to grant. If there are other grounds for rejection, the examiner states the matter in the “Remarks” section of the Notice of Preliminary Rejection (의견제출통지서) and recommends an amendment. [3] An applicant who cannot accept a matter amended ex officio must file a written argument by the time the patent fee is paid (Patent Act, Art. 66-2(3)). If a written argument is filed, that ex officio amendment is deemed never to have existed. In this case, the decision to grant is also deemed revoked. The exception is where only an ex officio amendment of the abstract is deemed never to have existed (paragraph (4) of the same Article). [1]

The Examination Guidelines state two cases that do not fall under the three types. One is where it is not clear whether “the” (상기) was written in error or the number of the claim referred to was written in error. The other is where all the claims referred to have been deleted. The Examination Guidelines treat both cases as non-compliance with Art. 42(4), subparagraph 2. [3]

Where it is not clear whether a statement falls under the three types, the Examination Guidelines state that it is desirable to notify it as a ground for rejection. The purpose is to give the applicant an opportunity to file a written argument and an amendment. If, on examining again in the light of the written argument and the written amendment, the examiner finds that the statement falls under the three types, the examiner cannot issue a decision of rejection on the basis of that statement. [3]

Consistent terminology is also connected with the support requirement. Technical terms in the description of the invention and in the claims can differ. Technical terms within the claims can also differ from each other. Where this results in a lack of clarity, the Examination Guidelines direct the examiner to notify a ground for rejection for non-compliance with Art. 42(4), subparagraph 1 (Part 2, Chapter 3, 5.(3)). [3]

Claims written by function, manufacturing process, parameter or composition ratio have their own criteria

A functional expression is not prohibited, but there is a condition. The Examination Guidelines state that a functional expression cannot be allowed unless the configuration of the invention is found to be clear as a whole despite the functional expression. [3] The Examination Guidelines give two cases in which the claim is accepted as clear. One is where a functional expression is needed because the technical idea is difficult to express clearly with conventional technical configuration alone. The other is where the meaning of the functional expression can be clearly determined from the description of the invention and the drawings (Part 2, Chapter 4, 4.(7)). [3]

A claim written with “means” or “step” is also examined under the support requirement. A specific configuration corresponding to the means or step must be in the description of the invention. If it is not, the Examination Guidelines treat the claim as a type not supported by the description of the invention (Part 2, Chapter 4, 3.(2)③). [3]

A claim that specifies a product by its manufacturing process is not deficient in the description because of that form alone. The Examination Guidelines accept the form “a product manufactured by the process of …”. The condition is that the configuration of the product is clear as a whole from that statement. However, the manufacturing process can be unclear even when the specification, the drawings and the common general technical knowledge at the time of filing are taken into account. In this case, the examiner can notify a ground for rejection under Art. 42(4), subparagraph 2. The same applies where the statement is so unclear that the structure or properties of the product cannot be understood (Part 2, Chapter 4, 4.(8)). [3] For the latter case, the ways in which the ground for rejection is overcome are set out. One is where the applicant proves special circumstances, such as that the product can only be specified by that manufacturing process. The other is where the applicant proves that the manufacturing process has no effect at all on the structure or properties of the product. [3]

A parameter invention is treated as not stated clearly and concisely unless four points are met. In the Examination Guidelines, a parameter invention is an invention in which a parameter that the applicant created at its own discretion forms part of the elements of the invention. It means a parameter that is not standard or not commonly used in the relevant technical field. It also includes a parameter formed by expressing the correlation between several variables as a formula. [3] The four points are as follows (Part 2, Chapter 4, 4.(9)). [3]

• The definition or technical meaning of the parameter can be clearly understood
• The value of the parameter can be clearly confirmed by identifying the measuring method, the measuring conditions, the measuring apparatus and the like
• The reason why that parameter has to be used is clearly shown
• The relationship with the state of the art at the time of filing can be understood

These four points are assessed in the light of the description of the invention, the drawings and the common general technical knowledge. Even if they are not stated explicitly, the claim is not treated as unclear if they are clearly understood from the common general technical knowledge at the time of filing. [3]

A composition whose composition ratio is stated in % is unclear if the sum of the amounts of the components contradicts 100%. The Examination Guidelines give four cases (Part 2, Chapter 4, 4.(10)). [3]

If the composition ratio is stated in parts by weight, the above requirements do not have to be met (Part 2, Chapter 4, 4.(11)). [3] Alloys are different. For an alloy, whether the claim is closed or open, the total of the composition ranges must neither exceed nor fall short of 100%. Limiting only the main component does not specify the claims, and all the remaining added components must also be limited. [3]

Category, number of claims and the manner of reference can also lead to rejection

A claim is treated as unclear if it is difficult to tell whether it claims a product invention or a process invention. In principle, the Examination Guidelines determine the category from the terms or expressions at the end of the claim (Part 2, Chapter 4, 4.(3)③). [3] The Patent Act defines the act of working differently for a product invention, a process invention and an invention of a process for manufacturing a product (Art. 2, subparagraph 3). [1]

The types also include a claim that only lists the elements without stating how they are combined, so that the invention is unclear. The same applies where the statement is too lengthy, for example because the same content is stated repeatedly (Part 2, Chapter 4, 4.(3)② and ④). [3]

If one claim states two or more inventions of different categories, a ground for rejection can be notified. The same applies where one claim claims two or more subjects. The example in the Examination Guidelines is “… a polymer compound and a contact lens using the polymer compound” (Part 2, Chapter 4, 6.3). [3] The basis is Art. 5(2) of the Enforcement Decree of the Patent Act (특허법 시행령), which requires the claims to be stated in a reasonable number according to the nature of the invention. [2][3]

A claim that refers to two or more claims must state the numbers of the claims referred to in the alternative (Enforcement Decree, Art. 5(5)). [2] The Examination Guidelines give “according to claim 1 or claim 2” as an example of a reference in the alternative. They give “according to claim 1, claim 2” and “according to claim 1 and claim 2 or claim 3” as examples that are not in the alternative (Part 2, Chapter 4, 6.5). [3] A claim that refers to two or more claims also cannot refer to another claim that refers to two or more claims (Enforcement Decree, Art. 5(6)). [2] The exceptions to these two provisions and examples are covered in a separate article, “Are multiple dependent claims allowed in Korea?“.

Non-compliance with the claim drafting requirements of Art. 5 of the Enforcement Decree is non-compliance with Art. 42(8) of the Patent Act and is a ground for rejection (Art. 62, subparagraph 4). [1] Art. 42(8) is not among the grounds for invalidation after registration. What Art. 133(1), subparagraph 1 of the Patent Act lists from Art. 42 is paragraph (3), subparagraph 1 and paragraph (4). [1] However, Art. 5(1) of the Enforcement Decree is a non-mandatory provision, and under the Examination Guidelines no ground for rejection is notified on the basis of that paragraph (Part 2, Chapter 4, 6.2). [3]

A computer program per se cannot be an invention. The Examination Guidelines list the subjects that are accepted as inventions where information processing by a program is specifically realised using hardware. They are an information processing apparatus, a method of operating it, a computer-readable medium on which the program is recorded, and a computer program stored on a medium. The last one applies to applications filed on or after 1 July 2014 (Part 3, Chapter 1, 4.1.8). [3] This is a question of subject matter eligibility, not of clarity.

Trademarks and product names also need care. In principle, the Examination Guidelines do not allow a trademark or product name to be stated in the specification. This rule is in “Other points to note” of Part 2, Chapter 3 (description of the invention) of the Examination Guidelines, and its wording is “specification” (명세서). The exception has three conditions. The product must be easy to obtain. There must be little possibility that the content of the invention changes because of a change in quality or composition. The product must be clearly identifiable (Part 2, Chapter 3, 5.(5)). [3]

On receiving a ground for rejection, fix by amendment; after registration, fix by correction

The specification can be amended until the certified copy of the decision to grant is served. After a notice of grounds for rejection, amendment is possible only in the periods set by the subparagraphs of Art. 47(1) of the Patent Act. [1] An amendment must be within the matters described in the specification or drawings originally attached to the written patent application (Art. 47(2), former part). [1]

An application filed in a foreign language has one more limit. An amendment of a patent application in a foreign language must also be within the matters described in the final Korean translation or the drawings originally attached (Art. 47(2), latter part). Captions in the drawings are excluded. [1] For an international patent application filed in a foreign language, the reference documents are different. The limit of the former part is the description of the invention, claims or drawings submitted by the international filing date (Art. 208(3)). The limit of the latter part is the final Korean translation or the drawings submitted by the international filing date (Art. 208(4)). [1]

An amendment that fixes an unclear statement is allowed even at the stages where the purpose of amendment is restricted. Those stages are an amendment in response to a notice of grounds for rejection under Art. 47(1), subparagraph 2 and an amendment made when requesting re-examination. At these stages, the claims can be amended in four cases only. One of them is clarification of an ambiguous description (“분명하지 아니하게 기재된 사항을 명확하게 하는 경우”, Art. 47(3), subparagraph 3). [1] If an amendment at these stages does not comply with Art. 47(2) or (3), the examiner must dismiss the amendment. The same applies where the amendment is found to have given rise to a new ground for rejection. Among amendments under Art. 47(3), subparagraphs 1 and 4, an amendment that deletes a claim is excluded from the latter ground for dismissal (Art. 51(1)). [1] The Examination Guidelines do not treat as a new ground for rejection the case where an amendment newly produces a statement that falls under the three types of obvious error. They provide that the amendment must not be dismissed on that basis (Part 2, Chapter 4, 4.(4)). [3] The timing of amendments is covered in “When can claims be amended in Korea?“. The restriction on purpose is covered in “What amendments are allowed after a notice of final rejection in Korea?“.

If a notified ground for rejection is not fixed, a decision of rejection can follow. In case 2014Hu1563, the applicant was notified of the ground for rejection concerning “preferably” (바람직하게는) twice, in the notice of grounds for rejection and in the decision of rejection. The applicant did not amend that part, and the Supreme Court held that it was difficult to find any error in the decision of rejection. [4]

After registration, the statement can be fixed by a trial for correction. Art. 136(1), subparagraph 3 of the Patent Act lists clarification of an ambiguous description (“분명하지 아니하게 기재된 사항을 명확하게 하는 경우”) as a ground for correction. [1] A correction must be within the matters described in the specification or drawings of the patented invention (paragraph (3) of the same Article). It cannot substantially extend or amend the claims (paragraph (4) of the same Article). [1] A trial for correction cannot be requested during certain periods, including while a trial for invalidation of a patent is pending before the Intellectual Property Trial and Appeal Board (특허심판원) (paragraph (2) of the same Article). [1] The respondent in that trial for invalidation can file a request for correction within the designated period (specified period) (Art. 133-2(1)). [1]

The amended Patent Act (Act No. 21955), promulgated on 15 September 2026 and scheduled to enter into force on 16 March 2027, does not change the articles of the Patent Act cited in this article. [1]

How Korea differs

The examination guidance of the United States and Europe also does not state that a claim becomes unclear merely because a specific phrase is used. The table below places the wording of the guidance of the three offices side by side.

US MPEP 2173.05(d) states that the mere use of “such as” or “for example” does not by itself make a claim unclear. It also states that the examples of phrases held to be unclear depend on the facts and should not be applied as rules in themselves. [6] MPEP 2173.05(b) explains that terms of degree do not automatically make a claim unclear. [6]

The EPO Guidelines for Examination, F-IV 4.9, deal with optional features. These are features preceded by “preferably”, “for example”, “such as” or “more particularly”. They are allowed if they do not introduce ambiguity. [7]

The composition ratio is where a difference appears in the wording. MPEP 2173.05(c) presents a court decision on a claim to a composition of A 20-80%, B 20-80% and C 1-25%. That decision held that the claim was not unclear simply because it could be read in theory to include compositions that cannot in fact be made. [6] The Korean Examination Guidelines give four cases, such as where the sum of the minimum amounts of all components exceeds 100%, as unclear statements. For a claim in the “comprising” form, they treat the two cases in which the sum falls short of 100% as clear statements. [3]

The standards of Japan and China were not checked against the original texts for this article and are not included.

What applicants should do

• In general, we suggest tidying up optional expressions in the claims before a Korean filing or entry into the Korean national phase. The parts joined by “preferably” (바람직하게는), “for example” (예를 들어) and “in particular” (특히) are the ones to look at. One way is to move the narrow range to a dependent claim.
• For words such as “about” (약), “approximately” (대략) and “substantially” (실질적으로), we suggest first checking whether there is a reason to keep them. If they are kept, it is advisable to confirm that the description of the invention contains a statement that fixes their meaning.
• For a numerical limitation that has only “… or more” or “… or less”, we suggest checking in advance whether the opposite limit can be found in the description of the invention. This is because an amendment can only be made within the matters described in the original specification or drawings. For an application filed in a foreign language, it is advisable to also confirm that the statement is in the final Korean translation.
• At the translation stage, we suggest checking that each element referred to by “the” or “said” (상기) appears once earlier in the claims. It is also advisable to use one term consistently across the claims and the description of the invention.
• For a composition claim stated in %, we suggest calculating the sum of the amounts of the components against the four cases. An alloy claim needs the same calculation even when it is written in the open form.
• On receiving a ground for rejection concerning clarity, we suggest considering an amendment together with the written argument, and not contesting by written argument alone. Please confirm the assessment of an individual case with a Korean agent.

FAQ

Is a claim always rejected if it uses “about”?

No. The Examination Guidelines give “about” (약) as an example of an expression whose degree is unclear. If its meaning is clearly supported by the description of the invention and there is no problem in specifying the invention, the claim is not treated as unclear. [3]

Can “A and/or B” be used?

The Examination Guidelines give “and/or” (및/또는) as an example of wording used with matter added optionally or alternative matter. The examiner assesses the “A and B” case and the “A or B” case separately. The examiner also considers whether one claim claims several inventions of different kinds. [3]

Can “preferably” be left in a claim?

Supreme Court Decision 2014Hu1563 dealt with a claim that joined a broad range and a narrow range with “preferably” (바람직하게는). The Supreme Court held that the claim did not meet the clarity and conciseness requirement. In that case, it was not clear which range was meant even when the description of the invention was taken into account. [4]

Is a claim rejected if “the” or “said” (상기) has no antecedent?

Where the invention is clearly understood when the claim is read without “the” (상기), it is treated as an obvious error. The Examination Guidelines provide that a decision of rejection must not be issued in this case. If it is not clear whether “the” (상기) is wrong or the number of the claim referred to is wrong, there is a ground for rejection. [3]

Does unclear language still matter after registration?

Yes. Non-compliance with Art. 42(4) is a ground for invalidation (Patent Act, Art. 133(1), subparagraph 1). The patentee can clarify an ambiguous description by a trial for correction. However, the correction cannot substantially extend or amend the claims (Art. 136). [1]

How DEFINE IP Law Firm handles this

DEFINE IP Law Firm checks claim language at the stage of preparing a Korean filing or entry into the Korean national phase. We check words that add optional matter, words of degree, the form of numerical limitations, and what each “the” or “said” (상기) refers to. For questions about claim language in Korean applications, please write to contact@defineip.kr.

Sources

1. Patent Act (특허법), Act No. 21134, in force from 11 November 2025. Articles 2, 42, 47, 51, 62, 63, 66-2, 97, 133, 133-2, 136 and 208; Addenda (Act No. 12753, in force from 1 January 2015) Art. 8; Addenda (Act No. 14035, in force from 1 March 2017) Art. 21. Compared with the version scheduled to enter into force (Act No. 21955, in force from 16 March 2027). https://www.law.go.kr/법령/특허법 (verified 9 October 2026)
2. Enforcement Decree of the Patent Act (특허법 시행령), Presidential Decree No. 35809, in force from 1 October 2025. Article 5. https://www.law.go.kr/법령/특허법시행령 (verified 9 October 2026)
3. Ministry of Intellectual Property (지식재산처), Patent Examination Guidelines (특허·실용신안 심사기준), MOIP Established Rule (지식재산처예규) No. 7, in force from 13 March 2026. Part 2, Chapter 3, 5; Part 2, Chapter 4, 3, 4 and 6; Part 3, Chapter 1, 4.1.8. https://www.law.go.kr/행정규칙/특허·실용신안심사기준 (verified 9 October 2026)
4. Supreme Court of Korea (대법원), Supreme Court Decision 2014Hu1563 Decided April 7, 2017 (대법원 2017. 4. 7. 선고 2014후1563 판결) [decision of rejection (patent)]. https://www.law.go.kr/판례/(2014후1563) (verified 9 October 2026)
5. Patent Act (특허법), former version (Act No. 11848), in force from 1 July 2014. Art. 42(4) and Art. 133(1), subparagraph 1. https://www.law.go.kr/법령/특허법 (version history, verified 9 October 2026)
6. USPTO, Manual of Patent Examining Procedure (MPEP) 2173.05(b) [R-01.2024], 2173.05(c) [R-11.2013], 2173.05(d) [R-07.2015]. Page update shown as 9 March 2026. https://www.uspto.gov/web/offices/pac/mpep/s2173.html (verified 9 October 2026)
7. EPO, Guidelines for Examination in the European Patent Office, April 2026 edition (in force from 1 April 2026), Part F Chapter IV 4.9. https://www.epo.org/en/legal/guidelines-epc/2026/f_iv_4_9.html (verified 9 October 2026)