der Grundsatz
principle
A fundamental rule, principle, or belief that serves as the basis for thinking or acting.
Ehrlichkeit ist ein wichtiger Grundsatz in unserer Familie.
Honesty is an important principle in our family.

principle
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principle
A fundamental rule, principle, or belief that serves as the basis for thinking or acting.
Ehrlichkeit ist ein wichtiger Grundsatz in unserer Familie.
Honesty is an important principle in our family.

The word is made up of 'Grund' (basis, foundation) and 'Satz' (here in the sense of theorem or principle). A 'Grundsatz' (principle) is therefore literally a fundamental principle.
Der Schutz der Menschenwürde ist ein wichtiger Grundsatz des Gesetzes.
The protection of human dignity is an important principle of the law.
Common verbs used with 'Grundsatz' (principle) are 'einen Grundsatz haben' (to have a principle), 'einem Grundsatz folgen' (to follow a principle), or 'gegen einen Grundsatz verstoßen' (to violate a principle).
Er handelt stets nach dem Grundsatz, immer ehrlich zu sein.
He always acts according to the principle of being honest.
The word 'Grundsatz' (principle) is often used in official, legal, or ethical contexts to express a fundamental rule.
Die Geschäftsführung hat neue Grundsätze für die Zusammenarbeit festgelegt.
Management has established new principles for cooperation.
The phrase 'im Grundsatz' (in principle) is used as an adverbial expression and means 'prinzipiell' (in principle) or 'im Wesentlichen' (essentially). If it comes at the beginning of the sentence, the verb follows in second position.
Im Grundsatz bin ich mit dem Vorschlag einverstanden.
In principle, I agree with the proposal.
reason / ground
'der Grund' and 'der Grundsatz' look similar, but they do not mean the same thing. 'der Grund' explains why something happens or why someone does something. 'der Grundsatz' is a basic rule or principle that guides how someone acts. So you can do something for a reason, but act according to a principle. The expressions can also be confusing: 'im Grunde' means roughly 'basically', while 'im Grundsatz' means 'in principle'. So pay attention to whether you mean a cause or a rule.

Ich habe den Grundsatz, im Urlaub keine Arbeitsmails zu lesen.
I have a principle of not reading work emails while on vacation.
Im Büro ist der Grund für die Verspätung schnell klar.
At the office, the reason for the delay quickly becomes clear.