When someone “posits” that person is putting forward an opinion or an argument that he believes to be true. Scientists posit many ideas or hypotheses (hipótesis). In Spanish a similar word would be “postular” o “proponer como principio que…”.
• Most religions posit that there is “life after death”.
• I posit that life is going to be different in many ways due to the Covid 19 virus.
So, if you are taking a Cambridge exam, for example, FIrst, Advanced or Proficiency, you may use “I posit that” rather than “I suggest that”, “I opine that”, and “I believe that”. Using a variety of such phrases will get you higher marks in the Cambridge Speaking test.