What's the difference between a period and an interval?


I’m always failing cards where the meaning is “period” and I type “interval” or vice versa. There is an uncanny amount of these in Wanikani so I guess there should be a reason that they are not marked as synonyms of each other… right?

Is there really a difference in meaning between the two terms as used in WaniKani?

For instance, is this something like Joda Time where Period is just an amount of time (e.g. 2 months) whereas Interval is also anchored to a specific start date (e.g. from Jul 20 2015 to Sep 20 2015)? Or maybe another completely arbitrary distinction that is never explained in WaniKani?

Also, sometimes both time period and period are valid answers wherease sometimes only one is valid. Is this こういち trolling us?


What’s the difference between interval and period in English? (To me interval is more general–its a chunk of space or time. Period is something like an interval that occurs in time) When I was learning these words in Japanese–I uncritically mapped them to their English equivalents given in their definitions and didn’t think about them much more than that.

I have no idea how 間 and 期間 are actually different or similar.


I haven’t gotten to these words yet myself, but as a native English speaker, I was taught and have always thought of an interval as sort of a passive span of time, like the time between two separate actions or between repetition of the same actions. I think this is because it shares a root with words like interim(in the meantime) and intervene(to interrupt, separate, prevent some action)

Period is more generic, but applies more to active spans of time in my mind. It describes a span of time for which something is actually happening.

So if I were to say I go to Japan for 1 week every 6 months, I would typically think of the 1 week as a period of time, and the 6 months as an interval of time. Of course, I’m sure these aren’t entirely correct, and I have no idea how they apply to the WaniKani usage of the terms, but this is how I personally think of the terms in my native language.


I should also say, the emphasis (for me) is on the action vs. non action, which may have been somewhat obfuscated by my example. It does NOT have to be between two actions for me to think of it as an interval. If somebody were to say ‘I’m going to Japan in 6 months’, I would think of this 6 months as an interval of time. During this time, they are not performing the action being described. It is a 6 month interval before they actually go (action) to Japan.


I like to add user synonyms for words like this, because the English translation usually doesn’t capture the nuance of the Japanese word, so I find it easier to group words with similar English meanings together when learning them here, and then learn the intricacies of their meaning once I see them used. I haven’t really seen 期間 used outside of wanikani before so I can’t attest to its meaning, but I do know that 間 is a grammatical word which is similar in meaning to the English word “during.” For example,
A transfer student came (during / in the middle of) class.


TBH those English words are really similar and there’s no reason to expect the Japanese words to have the exact same nuances. I’d look at what other synonyms WK gives, or when you get better at Japanese look them up in a proper dictionary.

But anyway. Here’s what Webster’s says:

A portion of time determined by some recurring phenomena
The interval of time required for a cyclic motion or phenomenon to complete a cycle and begin to repeat itself
A chronological division: stage

A space of time between events
A space between objects, units or states.

So interval is a length of time (like our SRS intervals) and a period is either a cyclical or repeating interval, or where you have multiple of those and name each one (like the Meiji Period).


To dovetail from what @kimera said, if you look at the some of the words provided for period and interval in a 国語 dictionary, you’re going to find some differences with regard to overlapping meanings and such. Let’s look at the definitions of 時期, 期間, 時代, and 間. (Rather than posting some of the lengthy definitions, I’m going to paraphrase them in English for the sake of time). Also, for clarity, I when I use Interval or period they are in reference to the definitions provided in the Merriam-Webster dictionary.

時期 - This word carries the meaning of 期間 and season within it, but also includes the meaning of carrying out something in a specified time. Also a certain demarcated period of time. Which carries the meaning of period (according to MW dictionary’s first definition)

期間 - This word had the shortest definition, essentially stating the period from one determined thing to the next determined thing. This is similar to interval, This carries a little of both interval and period’s meanings.

時代 - This carries the meaning of historical periods as well as past and present periods of time. This meaning overlaps well with one aspect of the English word , period.

間 - This word had the most definitions as that it’s a more generic word. This word encompasses the idea of temporal and spatial distance along with other specific uses which I won’t mention.

Although the overlap makes doing reviews a pain, the actual use of Japanese language is going to need a deeper understanding so one doesn’t misunderstand or misuse these words.