A declarative statement is said to be grammatically unmarked, since it typically starts with a subject followed by a verb and a verb complement can follow the verb if necessary. This is the most common and expected word order for a declarative statement. However, there are cases where the word order can change or be modified for emphasis or other purposes.
Pay attention to the examples:

In some cases, a sentence may appear to lack a subject, especially in spoken language. However, there may be a hidden subject that is implied or understood by both the speaker and the listener. Such sentences are typically formed through processes of ellipsis. Check out the examples:

In some cases, inversion might cause a sentence to begin with a verb before the subject is added, especially for emphasis. This can create confusion about whether the sentence is declarative or not. However, even if the subject is added later in the sentence, if the sentence is ultimately stating a fact or expressing an opinion, it is still considered declarative. For example:

Facts can be stated in both affirmative and negative forms. Negative statements, as the name suggests, include a negation using a negative marker. This is used to indicate the absence or non-existence of something or to deny a fact or assertion. For example:

Declarative sentences always end in a period (.).

Declarative sentences can be used in all tenses, including past, present, and future. The tense used in a declarative sentence depends on the context and the intended message that the speaker or writer wishes to convey. Tak a look at the examples:

Declarative sentences can be formed in both passive and active voices, depending on the intended emphasis and meaning. There is no limitation in this regard, as long as the intended meaning is conveyed clearly and accurately.