Ron Cephas Jones on the challenge of playing the William of Randall's imagination on This Is Us

For Ron Cephas Jones, season 4 of This Is Us presented a new challenge.

The series has already asked him to play over 20 years of age ranges and act out one of the most gut-wrenching deathbed scenes of the last decade. Then, in its most recent season, it asked him to imagine an alternate history for William, one that was entirely of Randall's (Sterling K. Brown) devising.

In episode 417, "After the Fire," Randall participates in a therapy exercise where he imagines both the happily-ever-after version of his life if Jack (Milo Ventimiglia) had survived the fire and a much darker, alternative history as well. In the dream fantasy, Randall met William much earlier in life, got his biological father into substance abuse counseling alongside Jack, and caught William's fatal stomach cancer early enough to save his life. The darker version imagined something far more crushing: a version of the story where William denied Randall's attempts to meet him and the two never developed a relationship.

For Jones, playing an off-kilter version of the character sprung from Randall's imagination proved difficult. "[That] kept tripping me up. Every time I went to do something I was reminded that it's not your interpretation, it's Randall's interpretation," Jones said during an interview as part of the SAG-AFTRA Conversations at Home series. "Both are very similar, but there are smaller nuances that I had to remind myself that it was Randall's idea/dream about how he thought William would react and that was the hard part, trying to get into Randall's head. I did work with the director really closely and the writer to dissect the words more and listen to them really carefully."

Jones says there were multiple times on set when he would question William's choices, down to where he was sitting in a scene. "I was like, 'He wouldn't do that, he wouldn't leave that out, he wouldn't have this thing on the kitchen sink because he would put it away before he answered the door and why are we seeing the stuff? Why am I sitting there? I usually sit here.' No, it's Randall's thing," he explains. "It was a lot of touch and go until I could get the rhythm of it."

For the scene where Randall and Jack come to William's apartment and William closes the door in their faces, Jones made the choice to look only at Jack. This would reinforce Randall's sense of being ignored and rejected. "There's no recognition, you won't acknowledge he's your kid," Jones says. "There were little meticulous things like that we put in there that resonated that made the difference between my interpretation and Randall's interpretation."

There was one other major factor that also changed the nature of the scene for him — it was the first time Jones was working onscreen with Niles Fitch, who plays the teenage/college-age version of Randall Pearson. "The energy he brought was so different from the energy I had felt before from Randall. I had never met and saw Randall at that age," he says. "I had to understand that I'm meeting my son in a way that I've never met him before and I've never acted in the series before... It was my first time seeing [Niles] as Randall, just as it was William's first time seeing him as Randall."

Watch the video above for more from Jones. This Is Us airs on NBC.

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