Be consistent in your choice of mood. A shift in mood without reason will confuse your reader. For example, do not combine an imperative clause with an indicative clause in the same sentence. See also Lack of Parallelism.
Read the instructions carefully [imperative] and you must assemble the
equipment completely [indicative] before
beginning the procedure.
Read the instructions carefully [imperative] and
assemble the equipment completely [imperative] before
beginning the procedure.
You must read the instructions carefully [indicative]
and assemble the equipment completely [indicative] before
beginning the procedure.
If you begin a description in the conditional (often regarded as a variety of the subjunctive), do not shift carelessly to the indicative.
One use for von Neumann machines proposes a single "space-seed" self-
replicating factory that could be sent to another world, where
upon landing it will collect raw materials and build more
copies of itself to accomplish some enormous engineering project.
One use for von Neumann machines proposes a single "space-seed" self-
replicating factory that could be sent to another world, where
upon landing it would collect raw materials and build more
copies of itself to accomplish some enormous engineering project.
--Kai Wu, "Artificial Life," SciTech Magazine (modified)
