Imperatives include jussives and optatives; jussives are those we normally think of as "commands" and can be either exclusive (in the sense that they exclude the speaker and usually have you as an "understood subject") or inclusive, in the first person plural. The jussive-exclusive type normally has a (S)VO o (S)VA form:
(13) Open the cover by turning knob B clockwise.
(14) Go to the blackboard.
(15) Remove without scratching.
The subject you is expressed when we want to single out one particular addressee in a group of people. For example, a teacher may point at a pupil in the class and say:
14a) You go to the blackboard.
Another case is when we want to emphasise the subject, usually with special overtones. For instance
14b) You be quiet!
may be understood to mean that the interlocutor has said something wrong, or done something bad, so s/he had better keep silent.
The inclusive type has Let's before V:
(16) Let's go to the cinema [Let's V A]
(17) Let's redecorate the house [Let's V O]
Optatives use Let (meaning permit, allow) followed by a subject in the third person:
(18) Let the children play in the garden [Let Sobl. V A]
Sobl. indicates that the subject of V is oblique, as a pronoun clearly reveals:
(18a) Let them play in the garden.
Some linguists include may-"volitives" in this group:
(19) May you be happy!
As examples 13 and 15 show, only the jussive-exclusive type is used in instruction manuals (where it is very frequent) and in other texts in technical or scientific English. From now on, the abbreviation ESP (English for Specific Purposes) will be used to refer to English texts of a scientific or technical type.