Ed Sheeran and Kendrick Lamar are both sure things for Grammy nominations for Song of the Year, as they are for Record and Album of the Year.

Sheeran could be nominated for either "Shape of You" or "Castle on the Hill." "Shape of You" will probably win the toss if only due to its ubiquity. It will be the Brit's fourth nom in this category in just six years.

Sheeran co-wrote "Shape of You" with Steve Mac and Johnny McDaid. (The song also carries a co-writing credit for the writers of TLC's "No Scrubs," due to a similarity.) Sheeran co-wrote "Castle on the Hill" with Benny Blanco. These two writers co-wrote Justin Bieber's "Love Yourself," which was a nominee in this category last year.

It's possible that both of these songs will be nominated, though the Nominations Review Committee, which determines the final nominations in the "Big Four" categories, would probably rather share the wealth. No songwriter or team of songwriters has had two nominees in this category in the same year since Elton John & Tim Rice scored 23 years ago with two songs from The Lion King. (That was the last year that rank-and-file voters determined the nominations.)

Lamar will be nominated for "Humble.," which he co-wrote with Mike Will Made It. It will be the second nom in this category for both writers. Lamar was nominated two years ago for co-writing "Alright." Mike Will Made It was a nominee here last year for co-writing Beyoncé's "Formation."

We're rolling out pieces in which we look at the likely nominations in the "Big Four" Grammy categories. We've already looked at Record of the Year and Best New Artist. Today, we focus on Song of the Year. Next up: Album of the Year. Then I'll huddle with fellow Grammy nerd Lenny Beer for a no-holds-barred conversation.

If both Sheeran and Lamar are sure things, that leaves just three open spots. As usual, there are more worthy contenders than there are openings. Here they are, in descending order of their perceived likelihood of being nominated.

Sam Smith's "Too Good at Goodbyes" has an excellent chance. Smith co-wrote the song with Jimmy Napes, with whom he shared the Song of the Year award three years ago for "Stay with Me." The members of Stargate also co-wrote "Too Good at Goodbyes."

James Arthur's "Say You Won't Let Go" is a tender, instant-classic ballad in the Sheeran mold. It contains one of the most vivid images in a pop song this year: "I held your hair back/when you were throwing up." Arthur co-wrote the song with Neil Ormandy and Steve Solomon.

Logic's "1-800-273-8255" (featuring Alessia Cara & Khalid) also has a good chance. The committee will want to applaud the songwriters' success at making the phone number of the National Suicide Prevention Lifeline as familiar to young music fans as the number of their local Domino's. The three artists co-wrote the song with Arjun Ivatury.

There are many other worthy songs if any of these presumed front-runners falter.

Kesha co-wrote the power ballad "Praying" with Ryan Lewis, Ben Abraham and Andrew Joslyn. Lewis was nominated in this category four years ago for co-writing "Same Love."

Sam Hunt co-wrote "Body like a Back Road" with Zach Crowell, Shane McAnally and Josh Osborne. This would be the first country song to make the finals since "Girl Crush" two years ago.

Harry Styles co-wrote "Sign of the Times" with Jeff Bhasker, Mitch Rowland, Ryan Nasci, Alex Salibian and Tyler Johnson. Bhasker received three consecutive noms in this category from 2011-13 for co-writing Kanye West's "All of the Lights," fun.'s "We Are Young" and P!nk's "Just Give Me a Reason."

Lady Gaga co-wrote "Million Reasons" with Hillary Lindsey and Mark Ronson. Gaga was nominated in this category for co-writing "Poker Face." Lindsey was nominated for co-writing Carrie Underwood's "Jesus, Take the Wheel" and Little Big Town's "Girl Crush." This would, surprisingly, be Ronson's first nom in the category.

As I've indicated, it's rare for a songwriter to have two nominations in this category in the same year. But Sheeran isn't the only songwriter who is vying to do that this year.

In addition to co-writing "Shape of You," Mac and McDaid co-wrote P!nk's "What About Us" (with P!nk).

In addition to co-writing "1-800-273-8255," Cara and Khalid each co-wrote other songs that are in the running. Cara co-wrote "Scars to Your Beautiful," which was a VMA winner for Best Fight Against the System. The song has the same empowering message as Linda Perry's "Beautiful," which was a 2003 nominee. Cara co-wrote the song with Warren Felder, Sebastian Kole and Andrew Wansel. Khalid co-wrote "Location" with Joshua Scruggs, Chris McClenney, Samuel Jiminez, Austsin Mensales, Olatunji Ige, Alfredo Gonzales, and Barjam Kurti. This would be the second year in a row that an R&B song has made the Song of the Year finals. As noted above, Beyoncé's "Formation" was nominated this past year.

In addition to co-writing "Too Good at Goodbyes," the members of Stargate co-wrote Julia Michaels' "Issues" with Michaels, Justin Tranter and Blanco.

In addition to co-writing "Issues," Tranter co-wrote Imagine Dragons' "Believer" with the members of the group plus the members of Mattman & Robin. "Believer" is vying to become the first rock song to be nominated in this category since Mumford & Sons' "The Cave" six years ago.

In addition to co-writing "Issues," Blanco co-wrote the aforementioned "Castle on the Hill."

Taylor Swift and Jack Antonoff co-wrote Swift's "Look What You Made Me Do" (which also credits the writers of Right Said Fred's "I'm Too Sexy"). Swift and Antonoff also co-wrote Swift's collabo with Zayn, "I Don't Wanna Live Forever (Fifty Shades Darker)" (with a third co-writer, Sam Dew).

In addition, Antonoff co-wrote Lorde's hit "Green Light" (with Lorde and Joel Little). All three of these writers are past winners in this category. Antonoff co-wrote fun.'s "We Are Young," the 2012 winner. Lorde and Little co-wrote her breakout smash "Royals," the 2013 winner.

Here are other key songs in the conversation.

Coldplay and The Chainsmokers' Andrew Taggart co-wrote "Something Just Like This." Coldplay won in this category nine years ago for "Viva La Vida."

Styles' 1D cohort, Niall Horan, is in the running for his appealing hit "Slow Hands," which he co-wrote with Alexander Izquierdo, John Ryan, Julian Bunetta, Ruth Anne Cunningham and Tobias Jesso Jr.

Childish Gambino co-wrote "Redbone" with Ludwig Göransson.

Lil Uzi Vert co-wrote "XO Tour Llif 3" with TM88 and John Lucas.

Rihanna co-wrote "Love on the Brain" with Fred Ball and Joseph Angel

Luis Fonsi and Daddy Yankee co-wrote their blockbuster hit "Despacito" with Erika Ender.

Bruno Mars co-wrote "That's What I Like" with Philip Lawrence and Christopher Brody Brown, among others. These three writers were nominated in this category for co-writing Cee Lo Green's "F**k You" and Mars' "Grenade." Mars and Lawrence were also nominated for co-writing Mars' "Locked out of Heaven." James Fauntleroy and members of The Stereotypes production team also co-wrote "That's What I Like."

SZA and Travis Scott co-wrote their hit "Love Galore" with Carter Lang, Cody Fayne and Tyran Donaldson.

My early picks: "Shape of You," "Humble.," "Too Good at Goodbyes," "Say You Won't Let Go," "1-800-273-8255."

Note: Last year, 1,033 songs were entered for Song of the Year, making it the most crowded of the "Big Four" categories. The nominations will be announced on Nov. 28. The awards will be presented on Jan. 28.

Check out Grein's predictions for Best New Artist