A LOT HEAT AND NOT MUCH LIGHT

• The most essential element in learning to talk science is mastery of the thematic patterns of each science topic. In order to teacher to make sense to students, they musto make conections between scientific thematics and the ways students already talk about a topic.
• In the classroom, there is always more than one thematic pattern woven into the talk. There is the standard scientific pattern of meaning relations, usualy implicit in how the teacher talks, and tehre are one or more alternative patterns that are voiced by the students.
• The way in wich science is mainly taught today leaves these patterns implicit most of the time, so that the differences between the patterns rarely get talked about directly.
• This is actually a very general and important point. Words do not necessarily "have" meanings in themselves. A word in isolation has only a "meaning potential", a range of possible use to mean various things. What it actually means as part of a sentence or paragraph depends on which thematic item in some particular thematic pattern it is being used to express.
• During a debate between teacher and student: readers of this dialogue can usually make sense of either the teacher's viewpoint or the students', but not often of both. It is hard to formulate the exact differences between their view. But when you use thematic analysis, you can see the details of the misunderstanding from line to line. The most useful way to picture these differences is to compare th thematic pattern diagrams for the two sides in the debate.

Diagramas de padrão temático

• Most semantic relationships connect two terms, so if we deaw a line between them in our diagram, we can label the line with abbreviations, borrowed from Halliday's terminology, for the kind of grammatical relationship that usually expresses their semantic relationship.
• The terms of a thematic pattern diagram should be called thematic items, or thematic terms, to distinguish them from words as such.
• The thematic items of a diagram are represented, of course, by words. But actually they are not words, they are the meanings that are expressed through the word. What I have loosely called 'terms' so far are more like abstract "concepts", in that each can be expresssed by many different words.