Difference between Happens and Occur

HAPPENS vs OCCUR: NOUN

To take place; come about. : happen.
To be found to exist or appear.
To come to mind.
To come to the mind; to arise in the mind; to suggest itself; to be presented to the imagination or memory; -- of an idea or thought.
To happen; to take place.
To meet; to clash.
To go in order to meet; to make reply.
To meet one's eye; to be found or met with; to present itself; to appear.

To run to, as for the purpose of assisting.
To run together; meet; clash.
To strike the senses; be found; be met with: as, silver often occurs native; the statement occurs repeatedly.
To emerge as an event into the actual world; happen; take place; come to pass; befall: as, what has occurred?
To strike the mind: with to.
Eccles., to coincide in time, so as to interfere each with the celebration of the other: as, two holy days occur.
To refer: with to.
Synonyms To come to pass, come about, fall out.
Suggest itself
Come to one's mind

Come about, Pass off, Bechance, Go on, Take place, Hap, Encounter, Chance, Pass, Bump, Hit, Find, Befall, Materialize, Occur

Affect, Erupt, Ensue, Recur, Arise, Come about, Go on, Pass off, Pass, Take place, Hap, Be, Come, Anticipate, Happen

Does, Goes, Occurs, Come about, Go on, Take place, Hap, Encounter, Chance, Pass, Bump, Hit, Find, Materialize, Occur

Materialize, Exist, Affect, Erupt, Ensue, Recur, Arise, Go on, Come about, Pass, Take place, Hap, Come, Anticipate, Happen

What Happens if None of These Caveats Apply?
What happens when an eviction case is appealed?
What happens after I fill out the papers?
But until that happens, here are some tips.
This often happens in October, November and December.
It happens all the time in my lessons.
What Happens After Your Loan is Paid Off?
There are a lot of other things that can be described here, but everything that happens in your pool happens in that cycle somehow.
When it happens, it is always to distinct individuals, and, after it happens, other victims are left behind.
Ollie because she happens to show up whenever a disaster happens.

Wars occur when sovereign nations challenge each other and wars do not occur when formerly warring parties are incorporated into a larger political unit.
This issue is more likely to occur where the employer is not a registered health practitioner, but can occur with any employer.
Although not every activity may occur for every migration, the steps that occur should generally follow the sequence shownbelow.
Should this occur at a population level, the effect on the emissions that occur within the City of Melbourne woulddramatic.
Surveillance can occur at any point in time and can often occur around your scheduled IME appointment times.
Most often, the problems occur during pregnancy; however, they may also occur during childbirth or shortly after birth.
Harassment, bullying, aggression and other bad behaviors occur when the culture facilitates the opportunity for them to occur.
Serious side effects can occur during treatment with this medicine and can sometimes occur without warning.
Atomicity ensures that either all actions occur or none occur.
Some environmental changes occur slowly, and others occur rapidly.