# Instruction patterns > This section covers the verbs and prepositions a document is written with. Page: PAG · Patterns Canonical: https://banes-lab.com/pag/patterns#instruction-patterns This section is stop 26 of 102 in the learning route. Previous: [16 - When rules collide](https://banes-lab.com/disciplined-methodology/plan/when-rules-collide.md). Next: [02 - From intent to structure](https://banes-lab.com/pag/patterns/intent-to-structure.md). It builds on [01 - Writing a first document](https://banes-lab.com/pag/guide/getting-started.md). This section covers the verbs and prepositions a document is written with. Each verb carries a [semantic contract](https://banes-lab.com/records/arch/semantic-contracts.md), and a document relies on that contract rather than on what a particular tool happens to do; a read, for example, leaves its source unchanged whichever tool performs it. [A1·a input verbs](https://banes-lab.com/pag/patterns#instruction-patterns-panel-a) lists what each input verb promises about its source, [A1·b output verbs](https://banes-lab.com/pag/patterns#instruction-patterns-panel-b) what each output verb promises about its result, and [A1·c control verbs](https://banes-lab.com/pag/patterns#instruction-patterns-panel-c) what each control verb promises about its effects. [A1·d three readers](https://banes-lab.com/pag/patterns#instruction-patterns-panel-d) shows who a contract serves, and [A1·e the prepositions](https://banes-lab.com/pag/patterns#instruction-patterns-panel-e) declares the relations the prepositions carry between the operands. A verb's contract together with its preposition is the whole meaning of a line. ### Verbs and their contracts A verb with no stated guarantee means whatever the model completes it as. A document says process the items, the model reads, filters, writes and deletes under that one word, and the reviewer cannot say which of those the author meant. A verb the model has seen carry one guarantee across many contexts is likely to carry it into the completion; a verb used loosely carries every meaning it has ever had. For this reason every line relies on its verb's contract and its preposition's relation, and a line whose behaviour breaks them is a defect in the line. The verb is chosen by the guarantee the line needs, rather than by the tool that will perform it. In practice, a read is used when the source must survive, an extract when its meaning must, a find when only existence matters, a filter when order must hold, and an execute when a side effect is the point. The operands are bound with the preposition that names their relation, and the guarantee is relied on downstream. To check this, read a line and state what it promises about its source and its result. A line whose promise you cannot state uses its verb loosely, and the repair is the verb whose guarantee matches the intent. A contract is a promise the grammar makes about the intent; whether the model or the tool executing the line keeps it is what [verification](https://banes-lab.com/records/arch/verification.md) is for. A contract promises one of three things: what happens to the source, what the result is, or what effects the line may have. Two contracts carry the most weight. An execute may have side effects, and saying so is what keeps each of them from being a [hidden side effect](https://banes-lab.com/records/arch/hidden-side-effect.md). A report is a statement to a reader, never a state that anything later reads as the truth. A line with the wrong preposition puts its operands in the wrong relation, and the model is asked to complete the relation it was given. A1·a input verbs ```pag READ FROM INTO # non-destructive · the source is unchanged LOAD FROM # acquisition with parsing EXTRACT FROM INTO # isolation · the source keeps its meaning FIND IN INTO # existence · boolean, non-invasive GLOB "" INTO # discovery by shape GREP "" IN INTO # discovery by content ``` A1·b output verbs ```pag WRITE TO # idempotent where it overwrites CREATE FROM USING