The phrase "a solid assumption" is correct and usable in written English.
It can be used when expressing confidence in a belief or conclusion that is based on available evidence or reasoning.
Example: "Given the data we have collected, it seems reasonable to make a solid assumption about the project's success."
Alternatives: "a strong assumption" or "a reliable assumption".
That was a very solid assumption since the birth of the internal combustion engine but now that we have electric cars and solar and wind power - it's no longer such a direct correlation.
In multi-solid (MS) wax models developed by Lira-Galeana et al. (1996), each solid phase is considered as a pure component which does not mix with other solid phases and can exist as a pure solid (solid assumption).
At least, that is now the solid assumption in Brussels and other European capitals, where the start of a new era in Greece – highly volatile, highly unpredictable – is taken as a given.
When Ms. Quinn, the Council speaker, entered the race in March, her candidacy was guided by a set of seemingly solid assumptions: that most voters were happy with the direction of the city; that her sizable lead was stable; and that the political embrace of Mayor Michael R. Bloomberg was assured.
Back up your projections with solid assumptions.
And "November," with Dylan Baker as the president's utterly cynical chief of staff, and Laurie Metcalf as a speechwriter scorned for her idealism, is based on the rock-solid assumption that the audience believes that politics is about money, spin and self-interest.
All results are proved in the settings of a solid cone, without the assumption of continuity of mappings.
The model of a drop resting on a solid base involves the assumption that a drop is sufficiently small (light) to allow its shape to be taken as that of a fragment of an ellipsoid of revolution.
"I still didn't know how to do the underlying computation to create the model, but I had a solid understanding of the assumptions that went into it.
