Simple Sentences:
* We can only speculate about the reason for her sudden departure.
* The news report speculated on the possible motives of the attacker.
* Experts speculate that the new technology will revolutionize the industry.
More Complex Sentences:
* While the official report offered no explanation, many people speculate that the accident was caused by human error.
* Although the evidence is limited, it's tempting to speculate about the existence of extraterrestrial life.
* It's dangerous to speculate about someone's intentions without understanding their perspective.
Remember: "Speculate" implies uncertainty. You're offering a guess or a possible explanation, but you don't have concrete proof.