How to perform != or <> in postgresql

i need to fetch the table1 content which is not present in the table2 i dont think which is possible by <> or != operator so can any one help me here

select t1._id, t1."categoryName", t1.company_id, t1.active from table1 t1
inner join table2 t2 on t1._id <> t2.category_id 
inner join table3 t3 on t2 .department_id <> t3 ._id where  t3._id = 1

via Schüler