ことがある・
This pattern says that something happens only sometimes, or that something sometimes does not happen. It is useful when describing intermittent events without presenting them as a regular routine.
Some occasions, not every occasion
The verb describes what happens on some relevant occasions. Those occasions may be stated directly—such as busy mornings or rainy days—or understood from context. The pattern does not specify an exact rate.
Affirmative and negative events
Frequency words can make the intended rate clearer, but the construction itself already presents the event as intermittent.
私はたまに、帰りに一駅分歩くことがある。
I sometimes walk the distance of one station on my way home.
Analyze忙しい朝は、朝食を取らないことがある。
On busy mornings, there are times when I do not eat breakfast.
Analyzeこの薬は、まれに強い眠気を起こすこともある。
This medicine can occasionally cause severe drowsiness.
Analyze祖母は今でも、昔の歌を口ずさむことがある。
Even now, my grandmother sometimes hums old songs.
AnalyzeChoosing between the two versions
ことがある and こともある overlap considerably. The second often suggests “there are also times when,” presenting the event as one possibility among other outcomes. It does not by itself mean a particular number of times.
One possible outcome
山の天気は、午後になると急に変わることもある。
Mountain weather can sometimes change suddenly in the afternoon.
AnalyzeThe sentence presents a sudden change as one possible outcome, not as something that happens every afternoon.
Do not confuse frequency with experience
Look at the verb immediately before the pattern. A nonpast verb gives the occasional-frequency meaning taught here. A past-form verb creates the separate experience pattern: it says that the event has happened before, not that it happens sometimes.
More examples
電車が遅れて、会議に間に合わないことがある。
Sometimes the train is delayed and I do not make it to the meeting on time.
Analyze在宅勤務の日でも、午後だけ会社へ行くことがある。
Even on work-from-home days, I sometimes go to the office just for the afternoon.
Analyzeこの地域では、春にも雪が降ることがある。
In this area, it sometimes snows even in spring.
Analyze疲れていると、目覚ましが鳴っても起きないことがある。
When I am tired, there are times when I do not wake up even if the alarm rings.
Analyzeオンライン会議では、音声が一時的に聞こえなくなることもある。
In online meetings, the audio may occasionally cut out for a short time.
Analyze出張中は、返信が遅くなることがあります。
While I am away on business, my replies may sometimes be delayed.
Analyze