The phrase "a defining theme and" is correct and usable in written English.
It can be used when discussing a central idea or motif that characterizes a work, concept, or situation, often in an analytical or descriptive context.
Example: "In her novel, the author explores a defining theme and the complexities of human relationships."
Alternatives: "a central motif and" or "a key concept and".
Thanks to Facebook's Cambridge Analytica scandal, and endless breaches by Uber and others, consumer data protection is likely a defining theme for 2018 and beyond.
If US climate diplomacy has had a defining theme over years and across presidencies, it is that its great rival China must be bound by the same conditions.
Disputes over transfers were a defining theme of the former Swansea and Watford boss' reign at Anfield, as the club's controversial 'transfer committee' system meant he did not have the full say on signings.
Krasikov's first collection of fiction, "One More Year," had just been released (her first published story, Companion," appeared in The New Yorker), and Lopate touched upon what he saw as a defining theme: the tension between the "old" and "new" worlds of a recent immigrant.
The decision by Obama to make economic inequality in general, and the minimum wage in particular, a defining theme of his second term in office and this year's mid-term elections has helped start a debate.
Looking back at many of the significant stories of 2015, this phenomenon emerges as a defining theme: some ephemeral line is crossed and suddenly an activity that had been regarded as unremarkable is vociferously rejected as intolerable.
A rebalancing of the commercial relationship between colleges and employers will be a defining theme.
Responsible research and innovation has become a defining theme of the European Horizon 2020 funding programme.
China's increasingly vocal and assertive posture was a defining theme of the meeting, as was the candid American acknowledgment that the recovery of the United States — essential for global economic growth — requires outside help.
Even while expressing confidence about Mr. Kerry's prospects, Democratic Party officials said they were concerned about what they described as his trouble in settling on a defining theme for his candidacy, the pace of his advertising and his progress in setting up field organizations in battleground states.
