系統 and 体系: grouped or connected systems and organized knowledge
Compare three plant lineages and an electrical-system fault with a grammar diagram and a legal framework. Read grouping, connections, and organized knowledge without inventing a taxonomy or a completed repair.
系統 for plant grouping and an electrical system
系統 (けいとう) occurs with a grouped or connected system. 「植物を特徴ごとに三つの系統へ分けた。」 means “We divided the plants into three lineages based on their characteristics.” Plants were divided into three groups described as lineages, using their characteristics.
「電気系統の故障を技術者が調べた。」 means “A technician investigated a fault in the electrical system.” The fault is what the technician investigated, and investigating is the action reported. Finding the cause or completing a repair is not separately reported.
体系 for organized grammar and legal knowledge
体系 (たいけい) occurs with an organized body of knowledge. 「文法の体系を図にして整理した。」 means “I organized the grammar system in a diagram.” The focus is the grammar system and the act of organizing it in a diagram.
「この講座では法律の基本体系を順に学ぶ。」 means “This course teaches the basic framework of law in sequence.” The legal framework is the learning subject, and 順に gives the sequence. No legal judgment about an individual case or advice for applying a law is supplied.
Find what is grouped, connected, or organized
The plant sentence presents three lineages grouped by characteristics. The electrical sentence presents a connected system whose fault was investigated. The grammar and law sentences concern organized knowledge and how it is arranged or learned. Identify the subject connected to each word.
Do not add names for the plant lineages or another classification system. In the electrical example, preserve the action 調べた as an investigation. These examples do not present a completed repair or explain a new biological taxonomy.
What is organized in the plants' three 系統 and in the grammar 体系 arranged in a diagram?
Show the answer and why
The first organizes plants into lineages by their characteristics; the second organizes a system of grammar knowledge. The electrical-system investigation is another use to read, without adding lineage names or a completed repair.