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Relative clauses (with e.g. 'which', 'that', and 'who')

Relative clauses are very useful in scientific writing as they can be used to define, specify or add information. However, their grammar is quite difficult.

Restrictive and non-restrictive relative clauses

(Adapted from Bottomley, 2021 )

Relative clauses can be restrictive or non-restrictive. This is illustrated in example (1) (Domone and Illston, 2010: 535):


Since the start of the industrial revolution in the late 18th century, there has been an exponential increase in our exploitation of materials for use in the technologies that have driven economic growth and increased the prosperity and living standards in much of the world. These advances have not, of course, been uniformly experienced owing to the wide variation in political, economic and social conditions in different regions and countries. Much of the growth has only been possible with the associated development and fabrication of infrastructure, which has required enormous quantities of construction materials with controlled and reliable properties.

The first clause in bold, beginning with that, is a restrictive relative clause. It specifies only those ‘technologies’ responsible for these effects; it does not refer to ‘technologies’ in general. Restrictive clauses can begin with that or which (that or who for people). In US English, only that is used.

The second clause in bold in example (1) is a non-restrictive clause, beginning with which. It refers to ‘the development and growth of infrastructure’ in general, adding some extra information rather than specifying a certain part of it. Non-restrictive clauses must begin with which (or who for people), and they must be separated from the main clause by a comma/commas as in example (2):

(2) The lecturer, who is very experienced, explains everything clearly.

Read here about common problems related to relative clauses .


Bottomley, J. (2021) Academic writing for international students of science. 2nd edition. Routledge.

Domone, P. and Illston, J. (2010) (eds) Construction materials: Their nature and behaviour. Spon Press, pp 414, 487.

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