The phrase "to fully fathom" is correct and usable in written English.
It is usually used when you are trying to explain the difficulty of understanding something, or questioning whether someone else understands something. For example: "It is hard to fully fathom the complexity of the human brain."
Neither sounded assured when interviewed on the Today programme; neither appeared to fully fathom the level of threat to the Labour party north of the border.
It seems impossible ever to give enough time to powerful art, to ever to fully fathom an installation by Richard Serra, let alone a painting by Rembrandt.
Argentines love their steak, but it is hard to fully fathom the country's fascination with cows until you walk down Avenida Boedo in the working-class Boedo neighborhood of Buenos Aires.
If you need a Hebrew and Yiddish glossary to fully fathom the diss — "krum" means "crooked," "haredi" means "fervently Orthodox," "tznius" is "modesty" and the "gedolim" are the great rabbis — then you have some sense of the almost claustrophobically inward community that Mr. Rosenberg chronicles.
Though it is definitely very beneficial, the 1-year Fellowship is probably too short to enable one to fully fathom the depth of a complex discipline such as stem cell biology.
However, it may be impossible to fully fathom the depth of trauma in living under the boot in Belarus.
"Only a small fraction of them will fully fathom them".
For examples of the latter, see "Psychology," "Little Things," or "The Nature of Friendship": Only after death do we fully fathom the distinctive qualities of a loved one, delve deeper into their essence, the living manifestations of which no longer disturb us.
Breasts come in all shapes and sizes, and a man can never fully fathom the changes that a woman's body experiences over a lifetime.
That's the way regulation goes and if Goldman is surprised by all this, it's yet more evidence that the firm doesn't fully fathom its power as a symbol of Wall Street practices that are now the subject of deep democratic revulsion.
Fact is, we humans are fallible, we make mistakes, we are not always kind with one another, we effect each other for better and for worse, life is not perfect, and it is all a much bigger mystery than we could ever fully fathom with our minds and desires.
