What is the Fifth Amendment that Donald Trump has invoked?

Mr Trump exercised his right not to give evidence that might incriminate him, something he said innocent people don't do

Former US president Donald Trump raises his fist outside Trump Tower in New York City . AFP

Former US president Donald Trump said he declined to answer questions during a New York state's civil investigation over his family's business practices.

The New York case is focused on The Trump Organisation — the former president's company that manages golf courses, hotels and other real estate — which has been accused of inflating the value of its properties.

In a statement, Mr Trump said he refused to answer questions “under the rights and privileges afforded to every citizen under the United States Constitution”, thus invoking his Fifth Amendment right — something he once said innocent people shouldn't have to do.

But what is the Fifth Amendment and what does it mean to “plead the Fifth”?

What is the Fifth Amendment?

In its simplest terms, the Fifth Amendment gives people the right to refuse to provide evidence that would incriminate them.

In “pleading the fifth”, a person declares they are exercising the right not to answer a question so as not to implicate themselves. Furthermore, an individual's silence or refusal to answer a question cannot be used against them in a criminal case.

Prosecutors also cannot argue to the jury that an accused person's refusal to answer a question implies guilt.

Witnesses can also plead the Fifth if they believe answering a question would implicate them in a crime.

Although the US Constitution states a person cannot be “compelled in any criminal case to be a witness against himself”, the right is also applicable in civil cases — such as the one facing Mr Trump.

The former president has, in the past, said that pleading the Fifth implies guilt, but it is a tactic that Trump ally Roger Stone and Mr Trump Jr employed when they were subject to questioning by the US House Committee investigating the January 6, 2021, attack on the Capitol.

Mr Trump's refusal to answer questions also signalled that he has changed course on his previously-held belief, citing his anger over an unrelated FBI raid of his Mar-a-Lago estate in Florida.

“I once asked, 'If you're innocent, why are you taking the Fifth Amendment?' Now I know the answer to that question,” he said.

Are there limitations to the Fifth Amendment?

The Fifth Amendment only applies to testimonial acts, so a person may decline to speak, nod their head or write a response.

But other pieces of incriminating information — such as a person's hair, DNA samples, fingerprints and blood — can be used as evidence in a case. Incriminating evidence that the person voluntarily provides is also not protected.

A person also cannot plead the Fifth as blanket protection for any question — answers to questions that would not help prosecutors are not protected by the Fifth Amendment.

Witnesses granted immunity can also be made to give evidence, as they can no longer reasonably fear prosecution.

In a civil case, a person can only invoke their Fifth Amendment right if they fear the evidence given could incriminate them in a later criminal case. If the person only fears being held liable in a civil case, then the protection is not granted.