BOSTON -- This morning, the justices of the Supreme Judicial Court turned their attention to a pointed question: when do words turn into manslaughter?

To the defense attorneys of Michelle Carter, the Plainville teenager accused of inducing her boyfriend's suicide through a stream of text messages that encouraged and cajoled him to kill himself, the answer was an almost unqualified "never."

"We contend that verbally encouraging someone to commit suicide, no matter how forceful the encouragement, does not constitute a crime in Massachusetts," attorney Dana Curhan said during the appeal hearing.

Without what Curhan termed "words plus" -- deception, as in the famous case of yelling fire in a crowded theater, or a threat -- encouraging someone to take action that results in their death is protected speech, he argued. No matter how reprehensible or how misguided, Carter's texts did not meet the legal standard of reckless conduct that prosecutors need to pursue a manslaughter charge, he said.

Bristol County Assistant District Attorney Shoshana Stern saw the matter differently, describing Carter's urgings as the emotional manipulation of a vulnerable, depressed young man that directly led to his death.

Asked by Justice Robert J. Cordy where the line was between speech and manslaughter, Stern cited a phone call between Carter and her boyfriend Conrad Roy moments before his death, during which Carter allegedly urged Roy, hesitant and scared, to get back in his truck and finish killing himself by carbon monoxide poisoning.

"It's very hard to draw a single line," Stern said. aWe can say that we know she was way over the line when she told him to get back into the truck. The prior actions are context for that."

Roy drove from his mother's house to a Kmart parking lot in July, 2014. He started a portable engine inside the cabin of his truck, and left it running until he died of carbon monoxide poisoning. A trail of text messages, released in an unsealed indictment, show that Carter repeatedly encouraged him to kill himself and urged him to follow through.

Prosecutors allege that Carter led a campaign of encouragement that directly led to the death of Roy, who had graduated from Old Rochester Regional High School that June.

"Carter assisted Conrad's suicide by counseling him to overcome his doubts," the indictment reads. "Her counsel took the form of positive direction, where she told him he was 'strong' enough to execute the suicide plan and would be happy once he was dead."

Michelle Carter's attorneys speak to reporters after SJC hearing 8 Gallery: Michelle Carter's attorneys speak to reporters after SJC hearing

The text messages included in court filings show Carter, in between professions of love, advocating for suicide as Roy's best option after an extended period of depression. "It's painless and quick," she wrote in one text. "Everyone will be sad for a while but they will get over it and move on," she wrote in another. She urged him not to delay the act, and advised him to find alternative methods of producing carbon monoxide when it became clear his truck's diesel engine would not work.

The appeal before the state's highest court comes more than a year after the case began, as defense attorney Joseph Cataldo's motion to dismiss the charges or have Carter tried as a juvenile has made its way from a Bristol County courthouse to the Beacon Hill chambers of the Supreme Judicial Court. The case has attracted national attention along the way, from media drawn to its sensational nature to law professors interested in its little-explored legal questions.

The justices asked probing questions of the state and Carter's defense team, testing the boundaries of what manslaughter-by-text could mean for state laws. Chief Justice Ralph D. Gants asked Curhan whether he believed urging someone to jump off a ledge was also not a crime.

"That's right," Curhan said.

What if there is emotional manipulation, Gants asked -- if one member of a couple says "If you love me, jump?"

It would still not constitute manslaughter, Curhan said.

Questioning Stern's defense of the manslaughter charge, Gants asked whether allowing the case to go forward could lead to charges for people who advise or encourage friends with terminal illnesses to take their lives.

Stern said she did not believe such encouragement would be criminal, and that the Carter case is "fact specific," with its long chain of communications showing Carter repeatedly telling Roy to end his life.

"The ultimately question is who's driving," Stern said. "She is pushing it harder."

Curhan and Cataldo, speaking to reporters after the hearing, said that Roy had long planned to kill himself and had a history of depression and previous suicide attempts.

Carter did not attend the hearing, Cataldo said.

The justices will also consider whether Carter should be charged as a juvenile or a "youthful offender," a category that allows for more severe sentences. Most of the oral arguments, however, focused on the definition of manslaughter.

According to New York Magazine, Roy and Carter had met years ago on vacation in Naples, Florida. As court documents show, they communicated and professed their love through a prolific stream of text messages, but rarely met in person. Roy's family told New York Magazine they only knew of a couple of meetings, and Joseph Cataldo, Carter's attorney, told MassLive last year that the relationship was almost entirely digital.