The Doctor surmises that the crack was caused by an explosion in time, which might have left "shrapnel" behind.

The Doctor surmises that if Kes can obtain the temporal phase shift that affected her, he would be able to stop her backwards progression in time.

The Doctor surmises that the minerals form a bio-reactive defence system triggered by the drilling operation.

The Doctor surmises that, thinking himself to be the last of his kind, Skaldak has nothing left to lose.

Doctors surmised early on that without the operation, she would not be able to live into her teens.

"Because his or her body would be born in this dimension, not Exosia," the Doctor surmised.

"For your penance, you must be their Caretaker," Balim said to the taller one, who the Doctor surmised was male based on the clothing.

The Doctor is now back on Skybase and surmises the Marshal to be mad.

The Doctor surmises that the Ood was being influenced by a being near them.

The Doctor surmised that only a single cell survived, which was then incubated in various hosts via biting them, passing down through the centuries until it matured.