This article will explain the difference between こと(Koto) and もの(Mono). Both words can be translated as “Thing” and have a similar meaning. Both words are expletive noun which represents abstract meanings and they are used with a modifier. Because of those similarities, two words tend to be confusing and be used interchangeably.
Difference between こと(koto) and もの(mono)
こと(Koto): things that are invisible and abstract
もの(Mono): things that are visible and concrete
Both こと(Koto) and もの(Mono) are expletive nouns in the grammatical rules. There are two types of nouns in Japanese. One is substantive nouns that have meaning by themselves such as 時計/とけい/Tokei/Clock and 洋服/ようふく/Yofuku/Cloth. Another one is expletive nouns that do not have meaning by themselves, such as こと(Koto) and もの(Mono), as well as ところ/Tokoro/place and とき/Toki/time. Expletive nouns such as こと(Koto) and もの(Mono) which do not have specific meanings by themselves are always used in conjunction with other words, adding connotations and grammatical functions to the expletive nouns. When used as expletive nouns, こと(koto) functions as a word to describe a situation or action and もの(mono) is used to describe an individual thing or an individual person. The word もの(mono) means an object with a “concrete” nature. The word こと(koto) means an abstract object, such as an action, property, or situation, or an object of thought or consciousness.
人間というもの/にんげんというもの/Ningen to iu mono/human beings
In this case, もの(mono) can’t be replaced with こと(koto) because もの refers to 人間/にんげん/Ningen/Human which is a substantive noun that has concrete nature and こと(koto) cannot be used for something that has a concrete nature.
目に見えること/めにみえること/Me ni mieru koto/What you can see
目に見えるもの/めにみえるもの/Me ni mieru mono/What you can see
In this case, こと(koto) can be replaced with もの(mono) but object expressed changes slightly. 目に見えること refers to an abstract situation in general while 目に見えるもの refers to something concrete that is right in front of you.
Definition of もの(mono)
An expletive noun that expresses a concrete thing
There are two other words that can be read as mono, one meaning a person 者 and the other meaning a thing 物, but as an expletive noun, they are written in hiragana もの.
The role of expletive nouns is to add nuance by being associated with other words. There is no strict boundary that separates the various meanings of もの(mono) and it is normal for them to have a mixture of meanings.
Definition of こと(koto)
An expletive noun that expresses an abstract thing, such as an object, thought or consciousness, situation or action
Specific events and circumstances are written in kanji as 事(koto) but other than that, it should be written in hiragana and writing them in kanji is wrong. Like もの(mono), こと(koto) is a word that can be used in conjunction with other words to produce various nuances.
Noun + こと(koto)
仕事のこと/しごとのこと/Shigoto no koto/About the job
This usage indicates the topic of the sentence.
This usage turns the verb into a noun, and it’s very common to see this usage.
I hope this article helped you understand the difference between こと and もの. These two seems to have a similar role in the sentence but misusing them makes the sentence sounds very unnatural. So keep their difference in mind.